e 07 operation

UN 5000 User’s manual

Chapter 7

Operation

Document number Lang. Rev. ind. Sheet

ABB Industrie AG 3BHS114940/E80 en 1

Contents:

7 Operation........................................................................................................................................................ 7-3

7.1 Introduction................................................................................................................................................. 7-3

7.2 Automatic voltage- and reactive power regulation of the synchronous machine.........................................7-37.2.1 The excitation system in the chain of the energy production 7-37.2.2 The synchronous machine on the network 7-37.2.3 The stationary behaviour of the synchronous machine 7-47.2.4 The dynamic behaviour of the synchronous machine 7-147.2.5 The transient behaviour of generator and network 7-17

7.3 Control and display elements....................................................................................................................7-207.3.1 General 7-207.3.2 Remote control (control room) 7-217.3.3 Analogue displays 7-327.3.4 Status and alarm messages 7-32

7.4 Local control.............................................................................................................................................. 7-347.4.1 Analogue value display 7-347.4.2 Fault display 7-357.4.3 Controlling the display 7-367.4.4 Printer key 7-367.4.5 Command keys 7-377.4.6 Service Panel 7-37

7.5 Operation of the system............................................................................................................................ 7-387.5.1 Checks before switching on 7-387.5.2 Switch-on sequence 7-397.5.3 Checks during operation 7-417.5.4 Shut-down sequence 7-417.5.5 Emergency-OFF 7-41



7 Operation

7.1 Introduction This part of the user manual describes how the excitation system has to be operated and which points need to be observed for fault-free operation of the system. This document mentions the necessary safety precautions and also contains a description of the operating behaviour of the generator and the operation of the excitation system in automatic and manual mode.

7.2 Automatic voltage- and reactive power regulation of the synchronous machine

7.2.1 The excitation system in the chain of the energy production

Coal, gas, water, wind, sun etc. are primarily used to produce electrical energy. This form of energy is usually converted first into mechanical and later in electrical energy using turbines and generators. For the conversion into electrical energy synchronous machines are mostly used, the output voltage of which is controlled by an excitation system. The electrical energy is then distributed to the centres of consumers via transmission lines.

Fig. 7-1 Excitation System in the chain of energy production

7.2.2 The synchronous machine on the network

In order to explain the automatic regulation in the excitation circuit of a synchronous machine, the behaviour of the synchronous machine itself under all possible operating conditions will first be examined in the following.

A regulated synchronous machine coupled to the network can be represented in simplified form in accordance with Fig. 7-2. The synchronous machine thereby represents the regulated object. All other components together form the regulator or excitation system. In



parallel operation with the network, the network influences the behaviour of the closed regulating circuit and in this sense acts as an external interference variable.

Fig. 7-2 Regulating circuit diagram

The characteristics of the synchronous machine and the network are largely predetermined. The excitation system only allows a correction of the overall behaviour in the sense of a technical optimisation. This is achieved during commissioning through adjustment of the corresponding regulating parameters.

In examining the behaviour of the regulated synchronous machine, a distinction must be made between the stationary and the dynamic behaviour of the synchronous machine. The stationary behaviour will primarily be addressed in the following, since this operating condition can be influenced by the operating personnel from the control room. A number of simplifications will be made and only those points will be examined which are relevant to the operating personnel.

7.2.3 The stationary behaviour of the synchronous machine

In examining the stationary behaviour of electrical machines, a distinction is made between

the electrical behaviour (currents, voltages) and

the mechanical behaviour (rotation, torque).

7.2.3.1 Electrical behaviour:

In order to describe the electrical behaviour in stationary operation, the synchronous machine can be described by means of the following simplified equivalent-circuit diagram.



Fig. 7-3 Equivalent-circuit diagram of the synchronous machine

The equivalent-circuit diagram is derived from the familiar representation of a voltage source with its internal resistance. The index d identifies the difference between the direct and transverse axis. The induced rotor voltage or EMK forms the voltage source behind the so-called synchronous reactance and depends on the rotational speed and the field current of the generator. Besides the synchronous reactance, which is composed of the main reactance and the control reactance, the ohmic resistance naturally also has an effect. For the purpose of examining the voltage regulation of the excitation system, the ohmic resistance can be disregarded.

In the plane of the drawing, the direction of the fluxes in the stator and rotor is identical. The torque is zero since no active power is being transmitted. This direction is described as the direct axis (d-axis). The direction perpendicular to this is called the transverse field axis (q-axis).

In addition, we must distinguish between two different types of rotor structure in synchronous machines:

salient-pole machines and

smooth-core machines.

The salient-pole machines (example shown in Fig. 7-4) have a large rotor diameter and are therefore used in slow-running drive assemblies such as water turbines with a rotational speed range of 20 to1500 rpm.

Fig. 7-4 Salient-pole machine

Two-pole (and some four-pole) generators of smooth-core design are used for fast-running drive assemblies such as steam and gas turbines with a rotational speed range >1500rpm, (see Fig. 7-5).



Fig. 7-5 Solid pole machine

The way in which both types of machine function is essentially identical. However, if one considers the simplified equivalent-circuit diagram in , the following should be taken into account:

For the Solid pole rotor design, the effective air gap in the d-axis and the q-axis is approximately equal, thus producing the reactances Xd Xq.

In the case of salient-pole machines, the magnetic resistances differ due to the unequal air gaps, so that : Xd > Xq.

These different characteristics have a direct influence on the operating range of the generator in network operation, as is illustrated in the following.



7.2.3.2 Operating modes of generators

Generators can be operated in the following operating modes:

No-load operation where there is no load on the machine

Machine under load in parallel operation with the network

Machine under load in island operation

Basically, the same relationships apply to the operating conditions of the loaded machines as to no-load operation . The sole difference is that the generator voltage is the dominant regulating variable in island operation and the reactive power is the dominant regulating variable in network operation.

The operating characteristics of the no-load machine and of the loaded machine in network operation are examined in the following.

7.2.3.3 Operation of the unloaded machine (no-load operation )

In no-load operation, the terminal voltage of the generator is equal to the induced rotor voltage. At constant rotational speed, this means that the terminal voltage depends directly on the field current. In the range up to nominal generator voltage, a more or less linear relationship exists between field current and generator voltage. When the generator voltage exceeds the nominal value, a saturation effect takes place which is essentially determined by the design of the stator iron. If one wishes to increase the generator voltage further, above its nominal value, the field current must be increased overproportionately.

Fig. 7-6 No-load characteristic

7.2.3.4 The loaded machine in network operation

If the machine is under load, a current flows in the stator windings which causes a voltage drop through the synchronous reactance. If the excitation current remains constant, the terminal voltage would therefore be reduced. Here, the excitation system has the function of preventing this drop in voltage by altering the excitation current.



Starting out from the equivalent-circuit diagram () we can now develop the vector diagram (Fig. 7-7).

Fig. 7-7 Vector diagram of the synchronous machine

Assuming that the generator is loaded with a purely ohmic load, the generator current IG is in phase with the generator voltage UG. As a result of the synchronous reactance Xd, a

voltage drop of U = Xd IG is caused via the direct axis which is perpendicular to the

terminal voltage. This defines the size and phase position of the induced rotor voltage EP.

According to the law of induction, EP is proportional to the rotational speed n and to the

magnetic flux in the air gap. The magnetic flux is, in turn, proportional to the field current, so that with a constant rotational speed, which is the case in network operation, the induced rotor voltage is proportional to the field current If.

We now change the nature of the load and assume a mixed ohmic-reactive load impedance of Z', whereby IZ'I is equal to the previous load R. The amount of the current remains the same, but it now lags behind the voltage by the phase angle . In order to maintain the generator terminal voltage, a higher induced rotor voltage EP (EMK) is

necessary. The generator therefore requires a higher excitation current.

The angle between terminal voltage and induced rotor voltage has a geometrical and a mechanical meaning. It describes the angle position of the magnet wheel relative to the rotating stator field and is therefore referred to as the load angle. This leads us to the second aspect of the synchronous machine, the stationary electromechanical behaviour. In parallel operation with other generators which are connected with an active network, completely different and new groups of questions arise such as: Where are the limits of synchronous energy transmission, identified by the terms synchronicity and stability? For this purpose we take a symbolic section through a two-pole machine in order to examine the torque characteristic (Fig. 7-8):



Fig. 7-8 Synchronising torque and load angle

Since the geometrical and electrical angles are the same in a two-pole machine, the phase diagram can be compared directly with the cross-sectional drawing.

For the first case, we assume that the rotating stator field has the same direction as the rotor field. At a rotor angle = 0, the transmitted torque is equal to zero. In the second case, the stator field is at a load angle = 45°. The mechanically-driven rotor now "pulls" the stator field along by means of magnetic force. To illustrate the force effect between rotor and stator, one can imagine a "rubber band". In stationary operation, the mechanical drive moment is equal to the electrical torque. For the smooth-core rotor, the maximum electrical torque is produced at = 90°. In reality, this working point cannot be used, because it is no longer stable. The rotor begins to slip in relation to the stator field. The generator falls out of step and becomes asynchronous.

The maximum torque is proportional to the induced rotor voltage EP (EMF, Electromagnetic Force Voltage) and to the stator current IG. Since the stator field has a sinusoid distribution, the torque formula for the solid pole machine can easily be derived.

M E IE U

Xd p Gp G

d

sin sin



Fig. 7-9 Torque characteristic

The entire range of possible stationary operating conditions is usually described by means of the power diagram (Fig. 7-10). This diagram can easily be derived from the vector diagram (Fig. 7-7). If one multiplies the voltage vectors by a vector Ug/Xd, the previous voltage vectors become power vectors and one obtains the power diagram shown below.

Fig. 7-10 Power diagram of a synchronous machine

Usually, only the upper semicircle is represented for generator operation. The circle around the co-ordinate centre point has a radius which corresponds to the nominal apparent power Sn. Sn is defined by the permissible temperature increase of the stator winding. The permissible operating range of a generator is limited in the active power axis by the drive limit of the turbine. Furthermore, the operating range in the reactive power



axis is limited, in the so-called overexcited range, by the thermal design of the rotor winding and, in the underexcited range, by the stability limit.

The overexcited range limit is essentially determined by the nominal excitation current. The sector formed by the field current with the centre 1/xd limits the overexcitement range. The nominal working point of the machine is derived from the intersection of the thermal limits of the stator and rotor.

In the underexcited range, the thermal loading capacity doesn’t play any role, but the important thing is to maintain synchronicity. As can be seen from Fig. 7-10, a safety zone must be maintained between actual and maximum torque. It follows from this that the maximum load angle may not be greater than approx. 70° - 80°. The load angle for any working point can be read from the diagram between the reactive power axis and indicator for the excitation power Pf.

Usually, synchronous machines are operated within the slightly overexcited reactive power range in order, on the one hand, to comply with the usual network conditions, and also to guarantee an adequate torque reserve in the event of network faults.

7.2.3.5 Functions of the automatic voltage regulator in network operation :

The voltage regulating system ensures automatic adjustment of the field current to the value which is necessary for the present operating condition. This means, on the one hand, keeping the operationally necessary values constant in stationary operation, and on the other hand carrying out a rapid adjustment if conditions change.

The basic electrical relationships will be explained with reference to the following structure of a power generating and distribution system.

Fig. 7-11 Network structure



A typical network structure consists of regional networks, usually with a ring-formed basic arrangement. These regions are linked together by transfer stations and form an interconnected network. Each network has feed points (power stations) and load points (substations). These substations usually feed a consumer network which laid out in a star-formed arrangement. In order to examine the system behaviour at a particular point, the actual network configuration is represented in greatly simplified form.

Fig. 7-12 Equivalent-circuit diagram of the network structure

The equivalent-circuit diagram shows the generator G, which can also stand for an entire power station, with the reactance XTr (transformer reactance) between generator

terminals and high voltage busbar. The resulting load impedance ZL relates to this feed

point. The rest of the system is reduced to an external reactance Xe and a voltage of the

rigid networks. All power-generating units are united at this point. The line resistances in the immediate vicinity can usually be ignored, whereas the capacity of longer transmission lines must be taken into account.

The basic requirements of the automatic voltage regulating systems which must be fulfilled in a typical network under stationary conditions, i.e. without faults, are:

1. The voltage at the consumer connection should be kept within acceptable limits.

2. Stable reactive power distribution in the case of several parallel-operated generators within the power station must be guaranteed.

3. The reactive power distribution within the network system should create minimal line losses, with good stability, also during load changes.

4. The generator should always be operated within the safe operating limits.

In order to achieve the aims of automatic voltage regulation under stationary operating conditions, it is necessary to partly correct the natural behaviour of machine and network. For this purpose, the voltage regulator is influenced with a value dependent on the current reactive current. The effect of this influence on the voltage regulation becomes clear if one applies the analogy of the frequency and active power regulation of the turbine.



Fig. 7-13 Reactive power regulation

As long as the generator is in no-load or island operation, the rotational speed (frequency) is maintained by the turbine regulator and the generator voltage by the voltage regulator. In parallel operation with an active network, frequency and voltage are primarily determined by the network and can only be altered to a small degree by the generator group. The secondary control variables, the active power and reactive power, now become the determining values in parallel operation .

However, an important difference exists between active power regulation and voltage regulation. The frequency is the same throughout the entire network. This is not the case with the voltage. Only the virtual "voltage of the rigid network" forms the value analogous to the frequency.

How would a generator coupled to the network behave if it attempted, with the aid of its turbine regulator, to keep the frequency of an entire network exactly constant? At the slightest underfrequency, the turbine would fully opened or in the event of underfrequency fully closed. Stable operation would be impossible. Only if we introduce a falling characteristic such that the rotational speed reference value is decreased with increasing power, it is possible to operate stably at any desired operating point. The active power is derived from the intersection of the characteristic with the system frequency. The rise in the characteristic is called frequency static and is defined as the ratio fn/f between no-load and nominal load.

With rotational speed regulation, this static influence always acts with falling characteristic. With voltage regulation, this static influence with negative characteristic is also introduced if generators without step-up transformers are coupled to a common busbar. In most cases, however, the generator is coupled to the network via a step-up transformer, so that a natural static with negative characteristic is produced through the transformer- and network reactance, see Fig. 7-13.



In such cases, the static influence is not falling, but is used to compensate the voltage drop via the step-up transformer.

It must be emphasised that the expression 'static' only means the relationship between the change in voltage and change in reactive power. This static must not be confused with the residual error in proportional regulating circuits. The deviation in regulation, equivalent to the setpoint-actual value difference, amounts to 0….0.5% in modern voltage regulators. The effective reactive power static can be set by means of parameters between –20% and +20%. Usual settings for the negative static are -4 to -10%, i.e. at 1 pu. reactive power, the generator voltage is reduced by the set value (e.g. 4%).

For positive values, the generator voltage is increased to compensate the current-dependent voltage drop via the step-up transformer.

Fig. 7-14 Static influence on the voltage regulator

For the operating personnel, it is important to know that the generator voltage changes through this static influence even if the setpoint is not changed from the control room.

7.2.4 The dynamic behaviour of the synchronous machine

The reactions of the synchronous machine to changes in the operating conditions are very complex. For this reason, in the following the behaviour of the synchronous machine in the event of changes will be considered in highly simplified form and in purely phenomenological terms.

Firstly the question: What type of changes can be expected?

on the network side: changes in voltage, frequency and load

from the drive shaft: changes in torque (load)

through faults: load dumping, short circuits, triggering of excitation

Usually, one only deals with the reaction of the machine to the change in a single parameter, because the relationships then remain simpler and easy to understand.

A distinction can be made between two groups of physical variables, which we will deal with separately, although they are not wholly independent of one another:

The first group comprises the electrical variables such as voltage, reactive power and excitation requirement (field current)

The second group is represented by the mechanical variables such as rotational speed or frequency, active power, torque and load angle.



We will start with the change in the electrical variables:

Let us assume that the network frequency and the torque of the drive shaft remain constant. The field current is also kept constant and the internal resistance of the field current source is disregarded .

What happens when a load is suddenly applied to the idling generator?

The effect varies greatly, depending on whether a change in active power or reactive power is involved. We will consider the case of a pure reactive power change, for example when an asynchronous motor is started up (Fig. 7-15):

Fig. 7-15 Reactive power surge for constant excitation current

For the unloaded generator, the terminal voltage Ug is equal to the induced rotor voltage Ep. After the circuit breaker S is closed, a reactive current IQ begins to flow immediately and causes a voltage drop through the generator reactance. The original magnetic flux, which passes through stator and rotor, cannot change instantly. The consequence of this is that a contrary current is induced in the rotor circuit via the air gap in order to compensate the changes on the stator side and maintain the balance of the circulation.

For the simplified equivalent-circuit diagram shown in this means that the direct axis reactance Xd is replaced by the transient reactance Xd', which is 5…10 times smaller than the synchronous reactance Xd.

7.2.4.1 The influence of the cage winding

Nowadays, almost all rotors of synchronous machines are equipped with a cage-like short-circuit winding similar to that of an asynchronous motor. This short-circuit winding, also called a damping winding, serves the purpose of electrodynamically damping the rotor oscillations. In the salient-pole design, solid pole caps or pole grids bring about a similar effect. The damping winding is coupled very closely to the air gap flux and its time constant is short. During the first 10 milliseconds, the induced compensation current practically only flows in this damping winding. The actual reactance is thus reduced in turn and is called subtransient direct-axis reactance Xd".

The time sequence of the dynamic processes is determined by the time constant T, which can be calculated from the relationship between the inductivity L and effective resistance R of the circuit. The subtransient time constant Td" is very short and we see it practically as a voltage jump without rise time. For the transient time constants, a distinction is made between no-load, unsaturated and short-circuited, saturated conditions of the machine, since the inductivity varies greatly with the degree of saturation.



The no-load time constant Tdo' is approximately three times greater than the short-circuit time constant Td'. The effective time constant for a machine under load lies between these.

In the case of the sudden loading with reactive power and constant excitation described above (excitation in manual mode), the terminal voltage drops, first with Td" and then with Td', to a value which is co-determined by the synchronous reactance.

If the generator voltage is regulated, i.e. the excitation operates in automatic mode, then in the event of a voltage drop the field current is automatically increased and the generator voltage brought back to its original value as illustrated in Fig. 7-16. How quickly the generator voltage recovers after the drop essentially depends on the type and design of the excitation system, i.e. whether this involves indirect excitation with an excitation machine or a static excitation system. The static excitation system displays a significantly faster reaction time than indirect excitation.

Fig. 7-16 Reactive power surge with voltage regulation (automatic mode)

In the case illustrated above, only the reactive power is influenced. The load angle therefore remains = 0. In Fig. 7-17, the same experiment is repeated with active power. In an earlier section it was recognised that the load angle is dependent on the active power. We will assume that the generator is already connected to a consumer R0. In this stationary condition, ignoring losses, the mechanical drive power PA developed by the turbine is equal to the electrical active power PE output to the consumer.



Fig. 7-17 Active power surge

If, by closing the circuit breaker S, the generator is now loaded with an additional active power R1, the electrical power of the generator is immediately increased. However, the drive power of the turbine initially remains unchanged and the balance between mechanical drive power PA and output electrical power PE no longer exists. The increase in the electrical power PE is primarily produced by the kinetic energy of all rotating masses which are coupled with the shaft. This means that the rotational speed decreases until the rotational speed regulator has increased the shaft torque by adjusting the quantity of gas, steam or water passing through the turbine.

Whereas under stationary conditions the electrical torque is in balance with the drive torque MA, the moment of inertia of the entire shaft arrangement d/dt plays a role during transient events. The following dynamic equation must be fulfilled at each instant:

7.2.5 The transient behaviour of generator and network

In the terminology of control engineering, all changes originating externally are described as "faults". There is a wide range with increasing influence up to serious interference with normal operation, which will be examined briefly in the following.



7.2.5.1 Types of faults affecting the generator

First, the difference between load change and load dumping should be mentioned: a change in load can go down to zero, but the generator circuit breaker remains closed. With load dumping, the generator circuit breaker is tripped, which means a change from parallel operation to island operation.

The generator short circuit is characterised by the electrical distance between the generator terminals and the location of the short circuit. A distance short circuit exists if the short circuit occurs somewhere between the busbar and the rigid network. On both the generator side and network side there are reactances which limit the short circuit current. The most serious loading of the generator is caused by the terminal short circuit. Short circuits near the power station lead to load dumping, which has to be triggered by the protective equipment. In the event of a remote short circuit, the network must be supported until the short circuit is eliminated by tripping of the network protection.

Load dumping: Immediate reaction by the automatic voltage regulator is required in the event of load dumping. The way in which the generator voltage changes in the time following opening of the circuit breaker is an important quality characteristic of a voltage regulator or excitation system.

Fig. 7-18 Load dumping

The decrease of the reactive power current to zero causes a spontaneous and

unavoidable voltage rise U = IQ . Xd". If, for example, the subtransient reactance is 0,2 p.u., the dumping of 0,5 p.u. reactive current produces an immediate rise by 10%, which cannot be reduced by any regulating action. Without an automatic voltage regulator, the voltage would then continue to rise until the maximum value is achieved, which is determined by the synchronous reactance. The rise time is dependent on the no-load time constant Tdo.

With a voltage regulator, this further rise is more or less completely prevented, and the voltage is restored to its original value. How quickly this is achieved depends on the type and design of the excitation system. Static excitation systems, which directly influence the field current of the generator, display the shortest reaction times, whereas indirect excitation systems have to overcome the additional time constant of the excitation machine. If the excitation system is operated in manual mode, the field current is regulated, which leads to an undesired rise in the generator voltage until the overvoltage relay of the generator protection is tripped and finally the generator is discharged. In order to prevent this, the setpoint value of the field current regulator is reset to the value of the no-load excitation current when the generator circuit breaker is opened.



A large drop in the generator‘s reactive power is also caused in the event of a distance short circuit.

Fig. 7-19 Distance short circuit

Such a fault at a remote electrical distance causes overcurrent and undervoltage, which can be permitted for a short period. The voltage regulator provides maximum excitation in order to support the voltage. At the instant the fault is eliminated by the selective protective equipment, the voltage rises again in accordance with the reduction in load. This overvoltage must, in turn, be adjusted to its original value by the voltage regulator.



7.3 Control and display elements

7.3.1 General

The UNITROL 5000 excitation system is an integral component of the power station installation. It is normally operated by remote control from the control room. The local control panel, directly on the front of the excitation system, is only used for commissioning and test purposes or as an emergency control option. If the power station installation features a higher-level control system, the commands to the excitation system are given by this power station control system.

The operating personnel must be familiar with the layout of the control and display elements and with the effects of the commands on the excitation system. Using these control and display elements, the operating personnel are in a position to adapt the generator, via the internal control and regulating circuits of the excitation system, to the operating conditions of the power station and/or of the network.

The excitation system is controlled in two ways:

REMOTE control from the control room with keyboard commands. The commands are passed to the excitation system as binary signals.

REMOTE control from the control room with monitor screen control. The commands are passed to the excitation system as binary signals or via a field bus.

LOCAL control using the local control elements integrated in the excitation system (local control panel).



The following table shows a summary of the commands available from REMOTE or LOCAL control. The right-hand column (Feedback Indication) shows whether a feedback indication is displayed in the control room.

Command Remote Local Feedback Indication

Exc. Circuit Breaker on Exc. Circuit Breaker off Excitation on Excitation off Control Channel 1 on Control Channel 2 on Operation Mode auto Operation Mode manual Setpoint Active Regulator raise max posSetpoint Active Regulator lower min posReactive Power Regulator on Reactive Power Regulator off Power System Stabilizer on Power System Stabilizer off Control local Control remote Lamp Test Release Start exciter breaker on Start exciter breaker off

The shaded areas of the local commands mean that these only become effective if the ENABLE key is pressed simultaneously on the local control unit.

In the following, the two forms of control REMOTE and LOCAL will be explained in detail.

7.3.2 Remote control (control room)

A number of control commands and a number of feedback indications are available in the control room for remote control of the excitation system. In addition, the most important status values of the excitation system and of the generator are displayed as analogue values. These command keys, signal lamps and display instruments in the control room which are required for control are not part of the UNITROL 5000 system.

The operating personnel must be familiar with the layout of the control elements and with the effects of the commands on the excitation system. Using these control elements, they are able to operate the generator, on the exciter side, according to the changing operating requirements, both in automatic mode (AUTO) and in MANUAL mode.

The commands from the control room are effective if the excitation system is switched to REMOTE. (see 7.3.4.2 page 32).



7.3.2.1 Commands and feedback indications

The commands and their effect on the excitation system and the generator are described in detail in the following.

Excitation breaker ON / OFF

The ON command closes the excitation breaker, as long as no Trip signal is active. Once the excitation breaker is closed the excitation can be switched on (see next section "Excitation ON / OFF").

The OFF command switches off the excitation breaker together with the excitation (see next section "Excitation ON / OFF"). The converter in the excitation system is thereby switched to AC converter operation (feedback of the field energy) and the discharge resistor is switched parallel to the rotor winding, so that the generator discharges quickly via the converter and the discharge resistor.

The excitation breaker can only be switched off remotely if the generator circuit breaker is already opened (generator is in no-load condition).

Excitation ON / OFF

The command EXCITATION ON is used to initiate the excitation of the generator. The excitation feeds the generator rotor with field current so that the generator voltage rapidly builds up to nominal voltage.

The On command remains without effect as long as a TRIP command is active. If the excitation breaker is still open when the command EXCITATION ON is given, this will be closed automatically. Only after the excitation breaker is closed is the excitation enabled and the field current begins to flow. A typical Start/Stop sequence for generators is shown in Fig. 7-20.

The following preconditions must be fulfilled for excitation to start successfully:

The excitation breaker must already be in ON position.

No Off command or Trip signal may be active.

The rotational speed should be greater than 90% of the nominal rotational speed.

If the converter transformer of the excitation system is supplied directly from the generator terminals, the auxiliary voltage for build-up of excitation must be present.

The command EXCITATION OFF switches off the excitation of the generator immediately. The converter in the excitation system is thereby switched to AC converter operation (feedback of the field energy) and the discharge resistor is switched parallel to the rotor winding, so that the generator discharges quickly via the converter and the discharge resistor. Parallel with the command EXCITATION OFF, the excitation breaker is also opened. After 60 s, the firing pulses to the converter are blocked so that this is completely blocked and switched off.

The excitation can only be switched off remotely if the generator circuit breaker is already opened (generator is in no-load condition).



Fig. 7-20 Sequence for excitation ON / OFF



After the excitation is switched on, the generator voltage typically builds up as follows

Fig. 7-21 Excitation process with soft start

7.3.2.2 Switchover between channel 1 channel 2

This excitation system features two completely independent regulating and control channels (channel 1 and channel 2). The two channels are completely equivalent, so that channel 1 or channel 2 can be freely selected as the active channel. The remaining stand-by channel (inactive channel) is always automatically matched to the active channel.

Fig. 7-22 Dual channel system with voltage regulator and current regulator

Basically, a channel change can be carried out at any time, except in the following situations:

If a fault is detected in the active channel, an emergency switchover to the second channel takes place automatically. It is then not possible to



switch back to the defective channel until the fault in the now inactive channel has been rectified.

A manual switchover from the active to the inactive channel is not possible if the inactive channel is defective.

In the event of a channel fault, a dynamic disturbance in the generator voltage can also occur simultaneously. However, the inactive channel (to which switchover takes place automatically at this instant) should not follow this dynamic disturbance in the generator voltage. In order to prevent this, the inactive channel follows the current generator voltage with a delay, and relatively slowly.

This relatively slow follow-up behaviour of the inactive channel must be taken into account in a manual switchover from the active to the inactive channel in that, immediately following a change in the generator voltage, the switchover is delayed for a short time. In this way, a surge-free switchover is achieved in every case.

7.3.2.3 Switchover between AUTO / MANUAL mode

The excitation system features an automatic regulator (AUTO mode) and a manual regulator (MANUAL mode) in each channel. In AUTO mode, the generator voltage is regulated so that as constant a voltage as possible is produced at the generator terminals. In MANUAL mode, on the other hand, the generator excitation (field current) is kept constant. With a fluctuating generator load, in MANUAL mode the generator excitation (field current setpoint) must be adjusted manually so that the generator voltage remains constant.

Basically, it is possible to switch between operating modes at any time, because the inactive regulator always automatically follows the active regulator. Special note should be made of the following:

If a fault is detected in AUTO mode ( emergency switchover to MANUAL mode), it is not possible to switch back to AUTO mode until the fault has been rectified.

The switchover from AUTO- to MANUAL mode is prevented if there is a fault in MANUAL mode.

The generator can operate in AUTO mode within extreme but permitted operating ranges which already lie outside of the permitted (and set) operating ranges for MANUAL mode. In these cases, the MANUAL regulator can no longer follow the AUTO regulator. The feedback indication AUTO/MANUAL READY allows the follow-up by the MANUAL regulator to be checked.

In the event of an automatic switchover to MANUAL mode due to a fault, switchover to the operating condition prior to the fault should take place. For this purpose, the follow-up control of the manual regulator reacts with a delay and relatively slowly to changes in the excitation current.

This relatively slow follow-up behaviour of the manual regulator must be taken into account in a manual switchover from AUTO MANUAL in that, immediately following a change in the excitation current, the switchover is delayed for a short time (wait for message: AUTO/MANUAL READY). In this way, a surge-free switchover is achieved in every case.



Note The MANUAL mode is designed as a special operation regu-lator (back-up regulator) and only functions as a field current regulator (no regulation of the generator voltage). In manual mode it is necessary that the excitation of the generator is expertly monitored by the operating personnel.

As long as the generator current and voltage transformer sig-nals are present, also in MANUAL mode an underexcitation limiter prevents a dangerous underexcitation of the machine which, in extreme cases, could lead to slipping. In addition, in no-load operation with reduced rotational speed, a V/Hz-lim-iter reduces the excitation and so prevents oversaturation of the machine and the connected transformers. The operating variables such as generator voltage, generator current and reactive power must be monitored by the operating person-nel and if necessary adjusted by changing the field current setpoint.

7.3.2.4 Switchover between AUTO / MANUAL mode

The excitation system features an automatic regulator (AUTO mode) and a manual regulator (MANUAL mode). In AUTO mode, the generator voltage is regulated so that as constant a voltage as possible is produced at the generator terminals. In MANUAL mode, on the other hand, the generator excitation (field current) is kept constant. In MANUAL mode, with a fluctuating generator load, the generator excitation (field current setpoint) must be adjusted manually so that the generator voltage remains constant.

Fig. 7-23 Single-channel system with voltage and current regulator

Basically, it is possible to switch between operating modes at any time, because the inactive regulator always automatically follows the active regulator. Special note should be made of the following:

If a fault is detected in AUTO mode ( emergency switchover to MANUAL mode), it is not possible to switch back to AUTO mode until the fault has been rectified.

The switchover from AUTO- to MANUAL mode is prevented if there is a fault in MANUAL mode.

The generator can operate in AUTO mode within extreme but permitted operating ranges which already lie outside of the permitted (and set) operating ranges for MANUAL mode. In these cases, the MANUAL regulator can no longer follow the AUTO regulator. The feedback indication AUTO/MANUAL READY allows the follow-up by the MANUAL regulator to be checked.



In the event of an automatic switchover to MANUAL mode due to a fault, switchover to the operating condition prior to the fault should take place. For this purpose, the follow-up control of the manual regulator reacts with a delay and relatively slowly to changes in the excitation current.

This relatively slow follow-up behaviour of the manual regulator must be taken into account in a manual switchover from AUTO MANUAL in that, immediately following a change in the excitation current, the switchover is delayed for a short time (wait for message: AUTO/MANUAL READY). In this way, a surge-free switchover is achieved in every case.

Note The MANUAL mode is designed as a special operation regulator (back-up regulator) and only functions as a field current regulator (no regulation of the generator voltage). In manual mode it is necessary that the excitation of the generator is expertly monitored by the operat-ing personnel.

As long as the generator current and voltage transformer signals are present, in MANUAL mode too an underexcitation limiter prevents a dangerous underexcitation of the machine which, in extreme cases, could lead to slipping. In addition, in no-load operation with reduced rotational speed, a V/Hz-limiter reduces the excitation and so prevents oversaturation of the machine and the connected transformers. The operating variables such as generator voltage, generator current and reactive power must be monitored by the operating personnel and if necessary adjusted by changing the field current setpoint.

7.3.2.5 Switchover to the emergency channel

In addition to the two main channels, the excitation system features two additional autonomous emergency channels.

Fig. 7-24 Main channel with emergency channel in a dual-channel system

The emergency channel, like the manual mode of the main channel, is equipped with a field current regulator. In addition to the field current regulator, the emergency channel is equipped with overvoltage protection and a gate control which is independent of the main



channel. The built-in overvoltage protection acts redundantly to the protective function built into the main channel. The operative effect of the field current regulator is identical to that of the field current regulator in the main channel, i.e. the emergency channel only regulates the field current and not the generator voltage.

The field current regulator of the emergency channel automatically follows up the leading main channel so that, in the event of a fault in the main channel, a jump-free switchover can take place automatically.

Manual switchover from the main channel to the emergency channel is only to be carried out by authorised specialist personnel. Switching back to the main channel can take place following tuning of the two regulators.

7.3.2.6 Switchover to the emergency channel

In addition to the main channel, the excitation system features an autonomous emergency channel.

Fig. 7-25 Main channel with emergency channel

The emergency channel, like the manual mode of the main channel, is equipped with a field current regulator. In addition to the field current regulator, the emergency channel is equipped with overvoltage protection and a gate control which is independent of the main channel. The built-in overvoltage protection acts redundantly to the protective function built into the main channel. The operative effect of the field current regulator is identical to that of the field current regulator in the main channel, i.e. the emergency channel only regulates the field current and not the generator voltage.

The field current regulator of the emergency channel automatically follows up the leading main channel so that, in the event of a fault in the main channel, a jump-free switchover can take place automatically.

Manual switchover from the main channel to the emergency channel can only be carried out using the service panel or PC tool and is only to be carried out by authorised specialist personnel. Switching back to the main channel can take place following tuning of the two regulators.



7.3.2.7 Reactive power regulator / power factor regulator ON / OFF

The reactive power regulator (Q) / power factor regulator (cosPhi) can be switched on if the AUTO mode is selected and the generator is connected to the network. The reactive power regulator / power factor regulator is superordinated to the voltage regulator and reacts only slowly to changes in the operating condition. Short-term network faults do not therefore influence this superordinated regulator and are absorbed by the voltage regulator. All limiters of the AUTO mode are enabled as before and if necessary dominate the voltage regulator including the superordinated regulator.

Fig. 7-26 Q-/CosPhi-regulator

The reactive power regulator / power factor regulator features its own setpoint setting (setpoint integrator). When the superordinated regulator is switched off, this setpoint setting always follows the actual value (current reactive power Q / current power factor cosPhi). This means that the transition from voltage regulator to superordinated regulator has no immediate effect on the operating point of the generator. Only when the setpoint (setpoint setting of the superordinated regulator) is later adjusted by means of the HIGHER-/LOWER commands (see 7.3.2.8), does the reactive power / power factor also change.

7.3.2.8 Higher / Lower (/) commands with feedback indications MIN / MAX

The / commands from the control room control the setpoints of both the operating modes AUTO and MANUAL / AUTO, MANUAL and the superordinated regulator. A setpoint is only adjusted by these commands if its operating mode is activated.

a) In AUTO mode

In AUTO mode, the setpoint of the generator voltage is adjusted by means of the / commands. In no-load operation, changing this setpoint adjusts the generator voltage, in operation under load this adjusts the reactive power. If the operating limits of rotor and/or generator stator have been exhausted, corresponding limiting regulators intervene and prevent the effect of the / commands in the direction of limitation.

If the setpoint for the generator voltage reaches its minimum or maximum setting value, the message "Active regulator MIN-POS / MAX-POS" appears. If the - and commands are given together, no adjustment of the setpoint takes place. When the excitation is switched on, the setpoint for the generator voltage is automatically set to its nominal value.



b) In MANUAL mode

In MANUAL mode, the setpoint of the field current is adjusted by means of the / commands. In no-load operation, this adjustment changes the generator voltage, in operation under load this adjusts the reactive power. In manual mode, only an underexcitation limiter (prevents slipping of the generator) and a V/Hz limiter (prevents magnetic saturation) are available. The / commands are not always prevented by a limiter as in AUTO mode. Care must therefore be taken to ensure that the operating limits of rotor and generator (according to power diagram) are never exceeded.

If the field current setpoint reaches its minimum or maximum setting value, the message "Active regulator MIN-POS / MAX-POS" appears. If the - and commands are given together, no adjustment of the setpoint takes place. When the excitation is switched on and when the generator breaker opens, the setpoint of the field current is automatically set to the no-load excitation current value (Ifo).

c) Reactive power regulator / power factor regulator

The slow reaction of this superordinated regulator (see 7.3.2.7) must be taken into account in adjusting the setpoint, otherwise lagging to an unplanned operating point could occur. In order to achieve better control over this setpoint adjustment, the reactive power setpoint / power factor setpoint is displayed in the control room.

If the setpoint of the reactive power regulator / power factor regulator reaches its minimum or maximum setting value, the message "Active regulator MIN-POS / MAX-POS" appears.

c) Reactive power regulator / power factor regulator

The slow reaction of this superordinated regulator must be taken into account in adjusting the setpoint, otherwise lagging to an unplanned operating point could occur. In order to achieve better control over this setpoint adjustment, the setpoint integrator of this regulator is therefore integrated in the control system in the control room. The output of the setpoint integrator supplies the remote setpoint (e.g. 4...20 mA) directly to the excitation system as setpoint for the reactive power regulator / power factor regulator.

If the remote setpoint is outside of the limit range, it is limited. The message "Active regulator MIN-POS / MAX-POS" is displayed if the external setpoint exceeds the internal limit range.



Fig. 7-26 Q-/CosPhi-setpoint

7.3.2.9 Power system stabilisation ON / OFF (if featured)

Low-frequency oscillations of the generator magnet wheel and / or the network frequency can be damped by means of the power system stabilisation (PSS).

Manual switching-on of the PSS is enabled as soon as the generator‘s active power reaches a certain settable value and the generator voltage lies within a settable range (e.g. 90-110% UGN). The power system stabilisation does not require any settings which have to be carried out by the operating personnel.

The PSS can be switched off manually at any time and is switched off automatically if the generator is outside of the set values for active power and voltage or is no longer connected in parallel with the network.

7.3.2.10 Switching off due to a fault (TRIP command)

In the event of a fault in the installation (e.g. in the generator protection), the excitation is automatically switched off and the excitation breaker opened.

Further procedure:

After the excitation has been switched off through a fault, the alarms on the fault display of the local control panel must be read off. The fault is to be rectified by authorised personnel. Further advice on troubleshooting is contained in section 8 "Maintenance and Troubleshooting “. Once the fault has been rectified, the alarms can be reset using the "Reset“ key. After the alarms have been successfully reset, the excitation can be switched on again.



7.3.2.11 Reset

If the message "Excitation System Alarm" is displayed in the control room, the fault text must be read from the local control panel and noted before resetting.

A fault which is indicated is reset using the remote reset. If the alarm message is not cancelled after resetting, it must be assumed that the cause of the fault has not been rectified. The reset key should not be pressed several times in succession, as each key-press is entered in the fault logger of the UNITROL® F device. Pressing the key too often fills up the fault logger and deletes the actual fault entries.

7.3.3 Analogue displays

Usually, only the excitation current signal is transmitted from the excitation cabinet to the control room. The other displays necessary for the operation of the machine, such as generator voltage, generator current, active and reactive power, are to be made available from the system.

7.3.4 Status and alarm messages

In addition to the above feedback indications, the following status and alarm messages are displayed in the control room:

EXCITATION BREAKER ONEXCITATION BREAKER OFFLOCAL CONTROL OVEREXCITATION LIMITER ACTIVE UNDEREXCITATION LIMITER ACTIVE ALARM MESSAGE READY FOR CHANNELTRANSFER

7.3.4.1 EXCITATION BREAKER ON / OFF

These messages show whether the excitation breaker is switched ON or OFF.

7.3.4.2 LOCAL CONTROL

This status message means: the system cannot be operated by REMOTE control.

Remedy:

Switch over to REMOTE on local control panel on the excitation cabinet.

7.3.4.3 UNDER/OVEREXCITATION LIMITER ACTIVE

An overexcitation limiter which reduces the excitation current or an underexcitation limiter which increases the excitation current is now active. The generator voltage regulator or the switched-on superordinated regulator is no longer effective. Operation with continuous limitation is permissible, but generally impairs the dynamic behaviour of the excitation system under changes in load.

Remedy:

If possible, deactivate limiter by adjusting the setpoint.



7.3.4.4 ALARM MESSAGE

The alarm message is a collective message for all faults in the excitation system. Detailed fault displays can be viewed on the local control panel of the excitation system.

If a fault occurs during operation, these fault messages must be noted and the service personnel notified. The system can generally continue to be operated with a fault; in the event of serious faults, automatic shutdown takes place. However, the system should not be started up after a shutdown until all causes of faults have been rectified and the alarm message has disappeared.

7.3.4.5 READY FOR CHANNEL SELECTION

A smooth switchover between channel 1 and channel 2 / AUTO- and MANUAL mode is only guaranteed if the message READY FOR CHANNEL TRANSFER appears.

7.3.4.6 READY FOR CHANNEL SELECTION

A smooth switchover between AUTO- and MANUAL mode is only guaranteed if the message READY FOR CHANNEL TRANSFER appears.

7.3.4.7 Field bus control

Any field bus control via a serial communications medium which might be installed is dealt with in a separate manual.



7.4 Local control

Fig. 7-27 Local control panel

The local control panel on the regulator cabinet contains 16 keys with LED's for the system-specific displays and controls, 10 control keys for the operating mode and internal functions and an LCD display with 8 lines, each with 40 characters.

The basic control of the excitation system can be carried out using the 16 keys with the status messages. Alarm messages and analogue values can be displayed on the LCD.

7.4.1 Analogue value display

A maximum of 64 pre-defined analogue values can be selected and displayed with the control panel. At the same time, either 8 analogue values in numerical form or 4 analogue values in 0-120% bar form can be displayed.

Analogue signals can be displayed as follows on the LCD display on the control panel:

Numerical display

When the key is pressed, 8 analogue signals appear with channel number, name of the signal, value and unit, and the yellow LED is lit. Further analogue signals can be displayed using the Scroll key.

Bar display

When the key is pressed, the first 4 analogue signals appear with channel number, name of the signal, value and unit, and with the associated bar. At the same time, the yellow LED is lit. Further analogue signals can be displayed using the Scroll key.



The 8 predefined analogue values which are displayed after initialisation are listed below:

Channel no. Value UnitValue 1 Generator voltage kVValue 2 Generator current kAValue 3 Active power MWValue 4 Reactive power MvarValue 5 Field current A-dcValue 6 Setpoint for AUTOMATIC CHAN-

NEL kV

Value 7 Setpoint for MANUAL CHANNEL A-dcValue 8 Actual value for generator voltage %

7.4.2 Fault display

There are various alarm and trip signals which describe faults or malfunctions within the excitation system. These fault messages can be grouped into alarms, protective switchover and tripping of excitation.

On the first fault message, the control panel automatically switches to fault message with display of the corresponding fault. The first fault which occurs (first fault) appears in the first line, the subsequent faults in the following lines. In addition, the LED on the RESET key flashes when the first fault is reported.

Fault messages

When the key is pressed, up to 8 fault messages appear, if faults are present (red LED is lit). The 1st fault always appears on the first line and the subsequent faults appear below this in ascending order of fault numbers. Further subsequent faults can be displayed using the Scroll key.

The following possible means of cancelling the faults are available:

Cancelling the fault messages:

All alarms are stored in the control panel. In addition, special alarms are also stored in the processor; these can only be reset by holding down the Reset key for a longer period.

RESET pressed briefly:

This cancels the fault display of the alarms stored in the control panel. If no alarms are active, the LED on the key goes out. If alarms stored in the processor are active, the LED changes from flashing to being lit continuously when the reset key is pressed briefly. If a new fault occurs, the alarm LED starts to flash again.

RESET pressed for longer than 1 second:

This resets both the alarms stored in the control panel and the alarms stored in the processor. If no alarms are active, the LED on the key goes out. If alarms are still active, the LED changes from flashing to being lit continuously when the reset key is pressed for longer than 1 second. If a new fault occurs, the alarm LED starts to flash again.



Caution All observations which could be of importance in connection with a fault (operating status of the power station, first fault display, further fault mes-sages, LED´s on devices etc.) must be noted before the RESET key is pressed or repair work can begin. Repair work may only be carried out by specially trained personnel.

7.4.3 Controlling the display

Cursor key

By pressing the Cursor key, one of the line positions 1...8 or 1..4 on the display can be selected. The current line is highlighted with the channel number shown in reverse contrast. When the last line is reached, it jumps back to the first line. The Cursor key is only active in the (numerical or bar display) analogue signal display.

Scroll key

When the Scroll key is pressed in the (numerical or bar display) analogue signal display, the channel number (in reverse contrast) and its analogue value changes.When pressed in the fault message, all fault messages in lines 2...8 move up or down by one position. The first line showing the first fault always remains in place.

Page key

When the Page key is pressed, the channel numbers change by 10 positions or the fault numbers by 6 positions. Otherwise functions like the Scroll key.

7.4.4 Printer key

When the Printer key is pressed, the analogue values in lines 1...8 are sent via the RS-232 serial interface to the printer (if connected). If fault messages are active, these are also sent. The yellow LED is only lit if data are being sent and the printer is ready to receive these. If the LED is flashing, the printer buffer is temporarily full.

In order to increase the service life of the LCD display, the display and background illumination are switched off after 60 minutes have elapsed without a key being pressed. The panel display is switched on again If one of the 10 function keys is pressed or if a fault message occurs.



7.4.5 Command keys

The control panel is equipped with a keypad. These keys allow the excitation system to be controlled locally in the same way as is possible remotely, from the control room. The commands are listed in the following table:

Command Local Feedback indication

Field breaker ON Field breaker OFF Excitation ON Excitation OFF Channel 1 ON Channel 2 ON Mode auto Mode manual Setpoint of active regulator higher max posSetpoint of active regulator lower min posReactive power regulator ON Reactive power regulator OFF Control local Control remote Lamp test Enable

The shaded areas of the local commands mean that these are only effective if the ENABLE key on the local control unit is pressed simultaneously.

7.4.6 Service Panel

In addition to the local control panel, a local service panel is also available. However, this is not used for local control of the excitation system. It simply assists the authorised service personnel in rectifying faults. Further information on the use of the service panel can be found in section 3.



7.5 Operation of the systemPrerequisites for safe operation:

The following prerequisites must be fulfilled for safe operation:

First commissioning successfully completed.

Periodical maintenance carried out in accordance with maintenance plan.

Any faults which have occurred have been properly rectified.

Any altered settings (parameters) have been checked and tested.

7.5.1 Checks before switching on

Before switching on, it must be ensured that all necessary supply voltages are present and that safe start-up is possible. The following checks must be carried out:

No maintenance work on the system is in progress.

Control and power cabinets are ready for operation and properly locked.

Generator output free, input and output cables to excitation transformer and to excitation cabinet are free (temporary earthing removed).

Battery supply for excitation breaker control and regulator supply present.

No alarm or fault messages active.

Excitation switched to REMOTE.

Excitation switched to AUTO mode.

Generator at nominal rotational speed (check rotational speed on display instrument).



7.5.2 Switch-on sequence

Action Display Control

1 Field breaker ON ON lamp is lit Field breaker is switched on

2 Excitation ON ON lamp is lit Voltage builds up in 5 - 20 seconds

GENERATOR RUNS WITHOUT LOAD

3 The excitation system is ready for operation under load.The generator voltage can be adjusted to the network voltage using the / keys.

Generator voltage is adjusted to setpoint.

4 When network- and generator voltage are synchronous, close generator circuit breaker.

Generator‘s reactive power re-mains close to zero.

GENERATOR IS OPERATING UNDER LOAD

5 Set desired reactive power within the operating limits of the generator using the / keys.

Generator voltage is regu-lated, the generator produces reactive power.



Fig. 7-28 On/Off switching cycle



7.5.3 Checks during operation

The following periodical checks should be carried out during operation:

a) In the control room:

No limiter active.

Setpoints of the active regulator are not at limit setting.

Channels are balanced, ready for switchover.

Excitation current, generator voltage and reactive power are stable.

The correct function of the field current regulator for MANUAL mode is continually checked by means of extensive monitoring devices. Nonetheless, it is recommended that, periodically, e.g. following start-up, this regulator be switched briefly in order to test that it is functioning correctly.

The correct function of the inactive channel is continually checked by means of extensive monitoring devices. Nonetheless, it is recommended that, periodically, e.g. following start-up, this regulator be switched briefly in order to test that it is functioning correctly.

b) On the excitation cabinets:

No active alarms.

No unusual noises.

7.5.4 Shut-down sequence

Action Display Control

6 Isolate the generator from the network by:- reducing the reactive power (through generator voltage set-point).– reducing the active power (via turbine regulator)– Open generator circuit breaker

7

&

8

Excitation OFF and Field breaker OFF

OFF lamp lights up

Generator voltage is reduced to 0 within a few seconds.

7.5.5 Emergency-OFF

Faults in a number of peripheral devices in certain cases can lead to a situation that neither REMOTE nor LOCAL control of the excitation system is possible. However, it must still be possible to switch off the excitation in an emergency. An emergency shutdown can be carried out using the local Emergency-Off pushbutton on the excitation cabinet // "External Trip" input on terminal X3 :19-20 / 22-23 (see also Hardware schematic, sheet 901).



An emergency shutdown switches off the generator and the excitation. However, the supply voltages for the excitation system are not switched off.

The operator must know how to carry out the emergency shutdown.

Caution With the generator circuit breaker closed, the excitation system cannot be switched off (by remote control) (the generator circuit breaker must be opened beforehand).The Emergency-OFF switch should only be used if it is impossible to switch off using the normal Off command.



e 07 operation

Documents