hitzinger ups details

I2NBDK10.DOCissue 00

06.06.2000eh

STROM. IM ENTSCHEIDENDEN MOMENT. POWER. AT THE RIGHT MOMENT.

Dipl. Ing. Hitzinger Ges.m.b.H. Helmholtzstraße 56 A-4021 Linz

Telefon Telefax

(0732) / 381 681 - 0(0732) / 381 681 - 5

Introduction to the Hitzinger

NBDK UPS System


NBDK UPS System I2NBDK-UPS

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issue 00 - page 2 /27

List of contents

1 INTRODUCTION ...............................................................................................................4

2 MECHANICAL DESIGN OVERVIEW ...............................................................................5

3 SCHEMATIC NBDK DIAGRAM........................................................................................6

4 UPS FUNCTION IN GENERAL.........................................................................................7

5 UPS FUNCTION................................................................................................................8

5.1 Operation modes of the UPS .................................................................................................................................... 8

5.2 UPS start up............................................................................................................................................................. 10 5.2.1 Starting from standstill ..................................................................................................................................... 10 5.2.2 Starting with the shaft revolving below 300 rpm ............................................................................................. 10 5.2.3 Starting with the shaft revolving between 300 to 700 rpm............................................................................... 11 5.2.4 Starting with the shaft revolving between 700 to 1500 rpm............................................................................. 11 5.2.5 Blank start ........................................................................................................................................................ 11

6 ENERGY FLOW..............................................................................................................12

6.1 By – Pass operation................................................................................................................................................. 12

6.2 Start up .................................................................................................................................................................... 12

6.3 Synchronisation....................................................................................................................................................... 13

6.4 Stand – by operation............................................................................................................................................... 13

6.5 Mains failure............................................................................................................................................................ 14

6.6 Diesel operation....................................................................................................................................................... 14

6.7 Mains return............................................................................................................................................................ 15

7 KEY COMPONENTS OF THE UPS ................................................................................16

7.1 Control Voltage ....................................................................................................................................................... 16

7.2 Clutch control circuit.............................................................................................................................................. 16 Typical torque transmission during mains failure.............................................................................................................. 17

7.3 Mains failure detection ........................................................................................................................................... 18 7.3.1 Mains voltage and phase rotation..................................................................................................................... 19 7.3.2 Mains frequency............................................................................................................................................... 19 7.3.3 Mains over-current ........................................................................................................................................... 20 7.3.4 Phase vector shift ............................................................................................................................................. 20

7.4 Alternator voltage regulation and supervision ..................................................................................................... 22 7.4.1 Voltage regulator.............................................................................................................................................. 22 7.4.2 Voltage control in redundant systems .............................................................................................................. 22 7.4.3 Alternator & AVR supervision......................................................................................................................... 22



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7.5 Speed governor........................................................................................................................................................ 23 7.5.1 Control loop considerations.............................................................................................................................. 23 7.5.2 Speed governor systems for redundant UPS's .................................................................................................. 24

7.6 Synchroniser unit .................................................................................................................................................... 24

8 SUPERVISION AND FAULT HANDLING.......................................................................25 8.1.1 Faults causing shut down ................................................................................................................................. 25 8.1.2 Faults causing synchronising shut down .......................................................................................................... 25 8.1.3 Bridging retarding faults .................................................................................................................................. 26 8.1.4 Bridging faults causing shut down ................................................................................................................... 26 8.1.5 Signalling faults ............................................................................................................................................... 26

8.2 Signalling of faults................................................................................................................................................... 27

8.3 Maintenance instructions ....................................................................................................................................... 27

9 REDUNDANT UPS SYSTEMS .......................................................................................27



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1 Introduction Rotary UPS systems with diesel engine are used to ensure a continuos consumer supply, for short term interruptions as well as long term mains failures. The NBDK system grants for extremely low frequency tolerances in the event of mains failure and for a high efficiency during stand-by operation. High availability and reliability of Hitzinger NBDK ´s are achieved because of large scales and careful selection of the individual system components. Due to the use of our well experienced PLC control units, malfunction or misuse is in fact impossible. Therefore the operation of the NBDK system does not require specialised personal. Further an extremely high quality standard is met because of our efficient internal quality assurance system. For a redundant UPS system two or more NBDK 's operate in parallel, which ensures additionally essential advantages, such as excellent dynamic voltage behaviour in case of sudden load application and increased frequency accuracy when mains voltage fails. Higher short term overload capability also is a further major aspect of Hitzinger parallel NBDKs. The aim of this paper is to give a service engineer the basic understanding of the UPS system. Providing the information needed for trouble shouting and fault finding in a comprehensive form. But it is not the intention of these paper to cover all possible faults or malfunction of our UPS systems. Since most high power UPS systems are designed according a customer's specification, the may vary from unit to unit. These alterations can be in the mechanical layout or in additionally function like an emergency power output or that auxiliary functions are incorporated in the UPS's PLC. However the functions and design hints common to all UPS systems are explained clearly in this paper, establishing a basic knowledge that a service engineer can rely on.



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2 Mechanical design overview

• 1 diesel engine • 2 electromagnetic clutch • 3 synchronous motor / alternator • 4 kinetic energy storage module • 12 flexible coupling A remote, electrically driven radiator is used for Hitzinger NBDK´s. It ensures to eliminate radiated waste heat during stand-by operation as well as to cool the engine during mains failure periods when the diesel engine is in operation. The electromagnetic clutch is brushless and is equipped with special friction linings. The magnet coil part does not turn in any mode. All bearings on the electrical machines are further equipped with thermometers. In stand-by mode, the synchronous machine acts as a motor, the electromagnetic clutch is deenergised and therefore open. The KINetic Energy Storage Module ( referred as KIN in the rest of the document ) is maintained in charged condition, The diesel engine also is kept in stand-by (standstill, while it is preheated and prelubricated). In case of mains failure the synchronous motor converts to alternator function, the diesel engine is cranked and started up the clutch is energised. During this period the alternator is maintained at is nominal speed by the KIN, the consumers are kept supplied continuously.

1212

1

2

3 4



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3 Schematic NBDK diagram

• 1 diesel engine • 2 electromagnetic clutch • 3 synchronous motor / alternator • 4 kinetic energy storage module • 5 alternator circuit breaker (optional) • 6 mains circuit breaker • 7 consumer circuit breaker • 8 by pass circuit breaker • 9 choke • 10 mains input • 11 consumer outlet

1 2 3 4

56 7

8

10 11

9



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4 UPS function in general Resuming that the UPS is in automatic operation, all faults are cleared and the alternator is running as a motor on the mains. The KIN is maintained in fully charged condition. The diesel engine is on standstill all auxiliaries like preheater, prelubrication etc. are working. During stand-by operation consumers and the synchronous machine are both supplied via the choke from the mains. Consumer frequency is equal to the mains frequency. The synchronous machine maintains the consumer voltage constant, irrespective of the mains voltage fluctuations. The reactive power of consumers is mainly supplied from the alternator . The power factor on the mains input is approx. unity. An unsymmetrical consumer current is equalised from the combination choke and synchronous machine to a symmetrically current drawn by all three phases on the mains input. Consumers harmonics back to mains or mains harmonics are largely filtered out. The choke suppresses interference voltage, witch may be produced by static discharge, lightning strokes, arching e.g. in the mains network, resulting in a voltage wise decoupling of mains and consumer. In the event of mains failure, the mains circuit breaker opens, the consumer circuit breaker remains on supplying the consumers temporary via the alternator driven by the KIN. The diesel engine is started, upon nominal engine speed the electromagnetic clutch is energised. The diesel engine supplies the consumer until the mains returns to normal conditions. If for any reason the diesel engine fails to crank with the starter motor, the electromagnetic clutch is energised starting the diesel engine ( high speed start ). On mains restoration, the consumers are synchronised back after a certain time delay period allowing the mains to become stable. The clutch opens and the diesel engine is shut off after an adjusted cooling down period.



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5 UPS function

5.1 Operation modes of the UPS The operation modes of the UPS are selectable via a lockable switch on the operator’s panel. The individual modes can be selected in the sequence the are mentioned below. In ‘’ OFF ’’ position the UPS is completely switched down with the PLC and all auxiliary equipment deenergised, except the battery chargers. The by – pass circuit breaker is on or switched on if off, this is performed by a hardwired circuitry. The UPS load is supplied right from the mains network. In ‘’ MANUAL ‘’ position the individual components of the UPS can be operated.

Attention:

It is in the operator’s responsibility if an interruption of the UPS output occurs, in case the circuit breakers are operated.

No damage or harm to the UPS itself can be done, due to wrong operation. All operations that are initiated by the operator, but not executable due to the actual status of UPS operation, are not proceeded, since the UPS is fully supervised by a PLC. A corresponding indication is given by the PLC. The indication can be either a flashing LED, a text readout or an other symbol on a terminal screen depending on the PLC unit used in the particular UPS system. This operation mode is to support a service engineer to maintain or test drive the UPS or individual parts of it and facilitates also in faultfinding. Since this operation mode is for maintenance and test only synchronisation of circuit breakers is not provided. In ‘’ BY – PASS ‘’ position the by – pass circuit breaker is switched on by the PLC. The aim of this operation mode is to ensure that the load on the UPS output is transferred to the mains, and to bring the UPS in a defined status when changing from manual operation to automatic operation or vice versa. The actual switching sequence depends on the history operation mode when switching to by –pass. When switching from ‘’ automatic ‘’ to '' by –pass '' with the mains available the by –pass circuit breaker is switched on and the consumer circuit breaker and if on, the mains circuit breaker are switched off. Is the mains circuit breaker off, then the mains circuit breaker will be synchronised before the by –pass circuit breaker is closed. This is a make before break transfer, no interruption on the UPS load occurs. In the case this operation is proceeded while no mains is available the consumer circuit breaker is switched off and the by – pass circuit breaker is switched on. There is no supply on the UPS output until the mains restores. In both cases the alternator and the KIN rolls off, the stored energy is controlled dissipated due to the friction loses in the system. The diesel engine proceeds with a cooling down period if it has been running before. When switching from ‘’ manual ‘’ to by – pass '' the consumer circuit breaker is switched off in case when it is on and the by – pass circuit is switched on. Be aware that there is no synchronisation of circuit breakers in this sequence. The clutch is deenergised if engaged and the diesel engine is stopped if running. The alternator and the KIN roll controlled off.



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In ‘’ AUTOMATIC ‘’ position the alternator is brought to nominal speed and the KIN is charged. If the KIN is fully charged the system is synchronised to the mains, then the by – pass circuit breaker is opened, supplying the UPS load via the choke from the mains. The clutch is deenergised and after a cooling down period the diesel engine will be stopped. The UPS is in stand by maintaining the output voltage within the specified limits and monitoring the mains input. When a mains disturbance is detected a diesel start is performed and the UPS load supply is transferred to the diesel engine – alternator. During the time period necessary for engine start up and load transfer the KIN delivers the energy needed and maintains the alternator shaft and therefore the UPS output frequency within the specified limits. Is the AUTOMATIC position entered while no mains is available, the by –pass circuit breaker is opened and the consumer circuit breaker is closed immediately after the alternator has reached nominal speed. In this case there is no synchronisation with the mains possible, the UPS load will be supplied from the alternator. After mains restoration and estimating that the KIN has already been charged, the UPS load is transferred back to the mains network as described. If at this moment the KIN is still charging the system waits until the KIN is fully charged before it proceeds with the mains synchronisation and load transfer. In automatic operation an uninterrupted power supply to the load is ensured. The UPS is fully supervised and monitored by the PLC, in case a malfunction or a failure is detected appropriate measures are proceeded. This measures correspond to the actual status of the system and may differ for a single failure whether the diesel engine is running or not, or whether the mains supply is present or not. Indications are always give to the operator. The PLC also ensures that the diesel engine is kept in '' ready to use '' condition while in stand by. This includes preheating and periodical prelubrication of the engine. In ‘’ LOAD TEST ‘’ position a few minutes lasting operation check is performed on the diesel engine at idle speed with the clutch disengaged prior a mains failure simulation is performed, in order keep the wear and stress on the diesel engine to a minimum. The UPS start and the UPS load transfer is executed in the same way as during a mains failure. If a mains failure occurs while a load test is conducted no interruption or disturbance occurs on the UPS load. The load test can be cancelled any time by switching the UPS back to automatic operation. The UPS will automatically return to stand by as soon as the mains condition this allows.



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5.2 UPS start up Before you read this section you should be familiarly with the basic function of the KIN Module. There are four different procedures for starting up the UPS depending on the actual operational status of the UPS. This are :

- Starting the UPS from a complete standstill. - Starting the UPS while the alternator is still rolling off with a shaft speed less

than approx. 300 rpm. - Starting the UPS with the alternator’s shaft at a speed within the range of

approx. 300 to 700 rpm. - Starting the UPS with the alternator’s shaft at a speed within the range of 700 to

1500 rpm. The speed values mentioned can vary for different units about 50 rpm depending on the made and type of the diesel engine, the alternator and KIN used.

5.2.1 Starting from standstill A few minutes lasting operation check is performed on the diesel engine at idle speed with the clutch disengaged to allow the diesel engine to get all bearings oiled before the heavy duty start is inducted. Then the diesel engine is stopped and the clutch engaged holding the shaft in standstill. The KIN mass is now accelerated to a speed of approximately 750 rpm by its wind – up – motor in order to prelubricate the KIN 's inner bearings prior to start up. Having reached this speed the starter motor ( the starter motor on the UPS’s diesel engine is either oversized or the engine is equipped with two starters ) is energised and accelerates the crankshaft, alternator and KIN shaft. At approximately 300 rpm, the diesel engine starts to fire and speeds up to idle speed, the starter is switched off and pulled out. From idle speed to nominal speed of 1500 rpm the speed governor ramps up corresponding to a pre-set rpm/min rate. The KIN mass is further accelerated to its final speed of about 2400 to 3000 rpm ( depending on the overall system specification and design ) from its wind – up – motor. By this energy is transferred in the KIN mass stored there as kinetic energy. Having reached the 1500 rpm on the shaft the alternator is excited and, if the KIN is fully charged, synchronised to the mains network, the clutch is disengaged and the diesel engine stops after a cooling down period. The UPS is in stand by.

5.2.2 Starting with the shaft revolving below 300 rpm Since the ignition speed of a diesel engine for industrial applications is around 300 rpm and speed matching is only possible above idle speed, actually no start can be performed. The system has to wait till the shaft has come to a complete standstill. After having sensed zero speed the system performs the start procedure mentioned. Long-term observations have shown that this is practically a very rare situation. Because it occurs only after a shut down period of approximately 3 hours. System shut downs usually are either for a short time or longer time periods for example over the week end.



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5.2.3 Starting with the shaft revolving between 300 to 700 rpm The shaft speed is above the ignition range of the diesel engine, but below idle speed and therefore speed matching is not possible. In this case the remaining kinetic energy in the system is utilised for cranking the diesel engine. Before that the speed of the KIN mass is measured and if it is above 750 rpm the clutch is engaged and the diesel engine is started. If the speed of the KIN mass is found to be below 750 rpm, the KIN mass is accelerated to this revolutions by its wind – up – motor prior the clutch is engaged. The starter motor is not used in this speed range. Since the crankshaft is accelerated above the ignition speed at approximately the same rate as during a start with the starter motor and disengaged clutch, no diesel run is necessary prior the start. From idle speed to nominal speed of 1500 rpm the speed governor ramps up corresponding to a pre-set rpm/min rate. The KIN mass is further accelerated to its final speed of about 2400 to 3000 rpm ( depending on the overall system specification and design ) from its wind – up – motor. By this energy is transferred in the KIN mass stored there as kinetic energy. Having reached the 1500 rpm on the shaft the alternator is excited and, if the KIN is fully charged, synchronised to the mains network, the clutch is disengaged and the diesel engine stops after a cooling down period. The UPS is in stand by.

5.2.4 Starting with the shaft revolving between 700 to 1500 rpm The shaft speed is above idle speed, speed matching is performed. The diesel engine is started with the clutch disengaged and ramps up from idle speed towards nominal speed, searching to match the alternator’s shaft speed. When both correlate ( there is a window of approximately 10 rpm difference allowed ), the clutch is engaged and the system is finally accelerated to 1500 rpm. It has been assumed that the speed of the KIN mass is also above the 750 rpm. If, for any reason, this is not the case, then the KIN mass will be accelerated to 750 rpm by its wind – up – motor prior the diesel engine is started. Having reached the 1500 rpm the alternator is excited and, if the KIN is fully charged, synchronised to the mains network, the clutch is disengaged and the diesel engine stops after a cooling down period. The UPS is in stand by.

5.2.5 Blank start Since clutch forced excitation is never used during normal start up, the same proceedings apply for a blank start were no mains is available. Except the requirement that the KIN mass has to be above 750 rpm before the shaft is accelerated to 1500 rpm is ignored.



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6 Energy flow

6.1 By – Pass operation

6.2 Start up

The UPS load is directly connected to the mains. The auxiliary supply of the UPS is taken on the output of the UPS. The diesel engine accelerates the alternator up to nominal speed. The KIN is charged from the UPS output. The energy (less friction losses) needed for the acceleration is stored as kinetic energy in the KIN. The UPS load is still connected directly to the mains.

preheater / prelubricationbattery charger

Mains input

Control panelfuel

Consumer

dies

el

engi

ne

reactive power KVAR

active power KW

P au

xilia

ry


Mains input

Control panelfuel

Consumer

dies

el

engi

ne

active power KW

reactive power KVAR

active power KW

P au

xilia

ry



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6.3 Synchronisation

6.4 Stand – by operation

The UPS load is transferred to the branch via the choke, then the by-pass circuit breaker is opened (make before break transfer). The synchronisation is performed with a slightly positive beat frequency, this ensures a smooth energy transfer, there may also flow same reactive current back to the mains due to choke magnetisation. After synchronisation the reactive power will be delivered from the alternator, the mains power factor becomes unity. Clean power is provided to the UPS load. The choke suppresses inter-ference voltage caused by static discharge, lightning strokes, arching eg. and harmonics are filtered out. In case of an unbalanced load the mains current is equalised. The mains power factor is kept to unity. - The synchronous machine runs as a motor on the mains, providing reactive power as demanded from the UPS load. The KIN is also kept speed in charged contitions.


Mains input

Control panelfuel

Consumer

dies

el

engi

ne

reactive power KVAR

P au

xilia

ry

active power KW

reactive power KVAR

active power KWac

tive

pow

er K

W

friction losses

reactive power KVAR


Mains input

Control panelfuel

Consumer

dies

el

engi

ne

reactive power KVAR

P au

xilia

ry

active power KW

frict

ion

loss

es



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6.5 Mains failure

6.6 Diesel operation

Immediately after a mains fault detection the mains circuit breaker is tripped and a diesel start is performed. The stored kinetic energy in the KIN is utilised for the diesel start and supplying the UPS load till the diesel engine can take over the load. The diesel engine supplies via alternator the UPS load and also transfers energy back to the KIN where it is stored as kinetic energy.


Mains input

Control panelfuel

Consumer

dies

el

engi

ne

active power KW high speed start

reactive power KVAR

P au

xilia

ry

active power KW


Mains input

Control panelfuel

Consumer

dies

el

engi

ne

reactive power KVAR

friction losses

P au

xilia

ry

active power KW



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6.7 Mains return

After mains restoration, the UPS load is transferred back to the branch via the choke, by synchronising the mains circuit breaker. The synchronisation is performed with a slightly positive beat frequency, this ensures a smooth energy transfer there may also flow same reactive current back to the mains due to choke magnetisation. After synchronisation the reactive power will be delivered from the alternator, the mains power factor becomes unity. Only active power is delivered from the mains supply. The clutch will be opened and, after a cooling down period the diesel engine is stopped. The UPS is back in stand by operation.


Mains input

Control panelfuel

Consumer

dies

el

engi

ne

reactive power KVAR

P au

xilia

ry

activ

epo

wer

KW

friction losses

reactive power KVAR

active power KW



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7 Key components of the UPS

7.1 Control Voltage The control voltage ( usually 24 VDC) is a battery back up system. There are separated batteries for the starter of the diesel engine and for the control panel itself. Both batteries do have individual battery chargers and supervision units. Additional the control battery is back upped from the starter battery. Under normal conditions these two batteries are separated by a rectifier diode and supply independently the designated circuits. In case the control battery fails the starter battery takes over supply of the control panel. The battery chargers are supplied from the UPS output, equipped with an electronic charging controller that ensures optimal charging and a maximum battery live time. Because of the recommended periodical load test of the whole UPS system, separated load circles are not necessary to be carried out on the batteries.

7.2 Clutch control circuit The performance of the UPS depends much on the reliability and on the energy transfer capability of the clutch. Therefore a careful selection of the clutch and its control circuitry is absolutely vital for the UPS availability and reliability. The clutch supply voltage is taken from the control battery ( is itself back upped by the starter battery ) and back upped by a transformer – rectifier unit. The transformer – rectifier unit is supplied from the UPS output. It delivers also the energy necessary for a high speed start. At high speed start the clutch is supplied with four times of it nominal voltage for approximately three seconds, in order to get the response time and transfer capacity necessary and to prevent the clutch lining from vitrifying ( forced excitation ). As mentioned earlier a high speed start ( forced excitation ) is only processed if the starter motor fails to crank the diesel engine at its first attempt.

0 1 2 3 4 5 6 7 8excitation time [ sec]

0

20

40

60

80

100

120

140

160

180

200

clut

ch to

rque

tran

smis

sion

[ pe

rcen

t of n

omin

al to

rque

]

Clutch torque transmission versus time at different excitation currents

nominal excitationcontinous operation

time limit

nom. excit. x 2

nom. excit. x 4



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7.2.1 Typical torque transmission during mains failure

Frequency response during mains failure

Motor speed Clutch torque

Limit

Limit

full load simulation600 KVA UPS system

nominal torque 100 % load

energy transfer into the System (mass of inertia etc.)l

high speed start

high speed start

diesel engine takes over load

nominal torque clutch7600 Nm



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7.3 Mains failure detection Detecting a mains failure as fast and as accurate as possible this is the most vital task of the UPS system. The whole performance of the UPS is relying on the mains failure detection. Also very dangerous are mains auto reclosing for synchronous alternators. The mains voltage returning after 300 ms can hit the alternator in asynchronous mode. A very fast decoupling in case of a mains failures for synchronous alternators in parallel operations to the mains is known as very difficult. Voltage supervision units cannot be used, because the synchronous alternator as well as the consumer impedance support the decreasing voltage. The voltage reaches the threshold of voltage supervision unit because of this reason after a couple of 100 milliseconds, and therefore a safe detection of auto reclosing in the mains is not possible with single voltage supervision units. UPS connected to the mains network

Mains input

Consumer

dies

el

engi

ne

High voltage grid

Point of mains monitoring( mains failure detection )



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Simplified schematic diagram

In stand by operation CB1 and CB2 are closed, at the point of mains monitoring the voltage Umains and Ualternator have the same value and are in phase. It is obvious that it is rather difficult to secure detect an mains failure. There are four electrical related criterions implemented for mains failure and mains outage detection. These are voltage and phase rotation, frequency, over-current and phase vector shift. All of them secure a mains failure recognition at different circumstance of failure occurrence. A additional criterion is derived from the KIN. If the KIN has delivered a certain amount of energy to the shaft of the alternator ( the speed of the KIN mass has declined ) while connected to mains, the reliability of the mains supply is not longer ensured and this is recognised as a mains failure.

7.3.1 Mains voltage and phase rotation The phase rotation supervision is only useful during set to work and therefore not always implemented. The voltage monitoring triggers if the mains network is still capable to supply the load, but the actual voltage level has shifted towards a figure ( either under-voltage or over-voltage ) where the UPS can no more maintain the output voltage within the specified values. At detection the mains circuit breaker is tripped, separating the UPS from the mains, and a diesel start is initiated.

7.3.2 Mains frequency The frequency monitor triggers if the mains network frequency is out of the specified limits ( either under-frequency or over-frequency ). Theoretically could this be the case when the mains network is still capable to supply the load, but this is very unlikely to be happened, when the UPS is supplied from a distributed mains network where many power stations share the network demand. A different and more likely situation occurs when the mains HV switch (CB2) trips and only a small load is supplied by the UPS. In this case the voltage at the point of monitoring is maintained within the limits due to voltage fed back from the alternator. Also no phase vector shift occurs because of the small load, triggering for mains failure. It is only the frequency that descents slowly while the energy is taken out of the flywheel. After having reached the under-frequency trigger the mains circuit breaker is tripped, separating the UPS from the mains, and a diesel start is initiated.

3~

point of mainsmonitoring

mains HV switch

to UPS load

mains input transformer

alternator

mains CB

to HV network

U mains U alternator

CB1

CB2



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7.3.3 Mains over-current When the mains circuit breaker ( CB1 ) trips due to over-current, a diesel start is initiated. This usually only happens when a short circuit occurs right on the UPS input . The mains circuit breaker's ( CB1 ) over-current release is automatically set back.

7.3.4 Phase vector shift The '' load angle '' of a synchronous machine is an exact and secure representation of the actual operation mode of the machine. It is a positive figure when operated as an alternator and a negative figure when operated as motor.

50 H

zfre

quen

cy

timetime scale depend on actual UPS load

under- frequency as mains failure trigger

CB is tripped and a diesel start is initiated

1

diesel engine is taking over load and accelerates

49 H

z

1 sec 2 sec 3 sec 4 sec 5 sec

48 H

z



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The '' load angle '' or rotor displacement angle α between stator and rotor is depending of the mechanical moving torque of the alternator shaft. The mechanical shaft power is balanced with the electrical fed mains power, and therefore the synchronous speed keeps constant. However a change in the load angle is recognisable as a phase modulation of the terminal voltage of the synchronous machine.

n1

N

SM

mag. flux

mag. axis ofstator flux

mag. axis ofrotor flux

n1

N

S

mag. flux



n1

N

SM

mag. flux



mag

. axi

s of

stat

or fl

ux

mag

. axi

s of

roto

r flu

x

mag

. axi

s of

stat

or fl

ux

mag

. axi

s of

roto

r flu

x

mag

. axi

s of

stat

or fl

ux

mag

. axi

s of

roto

r flu

x

Synchronous machine operation when connected to a infinitve mains network.

The magnetical axis of the stator flux is allways in phase with the mains.

A torque is applied on the shaft in the sense of rotation. The magnetic flux of the rotor (rotating DC field ) ‘’ pulls ‘’ on the stator’s field. Power is delicered into the mains network. The machine works as an alternator.

The ‘’ load angle ‘’ of the maschine is positiv and reflects the load. At 90 degree electrical (is not equal to mechanical degrees ) the machine has reaced it power limit. If more torque is applied, the machine pulls out of synchronism.

A torque is applied on the shaft against the sense of rotation. The magnetic flux of the stator ‘’ pulls ‘’ on the rotor’s field. Power is taken from the mains network and provided on the shaft. The machine works as a motor.

The ‘’ load angle ‘’ of the maschine is negativ and reflects the load. At 90 degree electrical (is only equal to mechanical degrees in a two pol machine) the machine has reaced it power limit if more torque is applied, the machine pulls out of synchronism.

No torque is applied on the shaft. The magnetic flux of the stator and rotor are in line. No Power is taken from the mains network nor is power delivered to it. ( Assumes an ideal machine with no losses )The ‘’ load angle ‘’ of the maschine is zero.

mains outage



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The vector shift relay measures the phase voltage and stores and updates a floating average value. This value is compared with the actual measured value on a circle by circle base. If a change in the period time greater than the adjusted window is detected the relay trips. As shown the vector shift relay detects a mains failure accurate and reliable while the alternator is parallel with the mains network. The threshold window is necessary that the relay does not triggers at load steps. At detection the mains circuit breaker is tripped, separating the UPS from the mains, and a diesel start is initiated.

7.4 Alternator voltage regulation and supervision

7.4.1 Voltage regulator The alternator is equipped with an electronic Automatic Voltage Regulator ( AVR). That regulator maintains the UPS output voltage within the specified values. The point of regulation is at the UPS output before the consumer circuit breaker, because of the choke connected to the mains in stand by operation, no power factor regulation is necessary in order to maintain the mains power factor to unity.

7.4.2 Voltage control in redundant systems For redundant systems where two or more alternators run in parallel, a cross current compensation is necessary in order to get a proper reactive load sharing. For cross current compensation current transformers are installed and connected to the respective regulator, producing a voltage droop corresponding to the reactive current delivered. Then the finish of the first CT ( first unit ) is connected to the start of the second CT (second unit ), the finish of the second CT is connected to the start of the third CT and so on , finally the finish of the last CT is connected to the start of the first CT. For the working principal we consider two alternators being parallel. If one alternator is loaded with reactive power, the excitation of this alternator is reduced due to the droop characteristic, resulting in a reduced reactive load delivery. Simultaneously the CT of this machine is routed to the second machine where it is connected inverse. This means the excitation of the second machine is increased when the first machine is reactive loaded, taking over reactive power. This mechanism ensures reactive power share of all alternators connected in parallel, while the output voltage is kept constant. The CT's are shorted out on the alternators not running or in non parallel operation.

7.4.3 Alternator & AVR supervision Each alternator is equipped with a voltage and a frequency supervision, triggering at under – voltage / frequency and over – voltage / frequency. Additionally on redundant systems where two or more alternators run in parallel an AVR supervision is installed. Because in parallel operation, even if one AVR completely stops working the bus bar voltage is maintained constant from the remaining machines. The alternator with the faulty AVR becomes an inductive load on the bus bar. The AVR supervision monitors the voltage on the excitation field winding of its respective alternator, if the voltage goes out of a certain window a malfunction of the AVR system exists and the unit triggers. The lower limit is determined by the none load excitation , the higher limit is determined by the excitation at specified overload of the alternator.



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7.5 Speed governor

7.5.1 Control loop considerations Depending whether the clutch is engaged or not, the characteristic of the speed control loop changes dramatically.

Therefore a separated set of speed governor parameter must be used for each situation. It has been shown that as a minimum requirement the gain of the governor must be changed when the clutch is closed. Operation with common settings for stability and dead -time compensation, but different gain at clutch opening or closing is applicable. Preferable speed governors with complete independence sets of parameters are installed. The speed sensor for the feedback to the speed governor is mounted after the flexible coupling. This prevents insertion of torque vibrations caused from the firing of the individual strokes as interference in the speed control loop.

flexible coupling

diesel engine

electromagneticclutch

electromagneticclutch housing

speed sense for governor is taken at this point

clutch control

control loop with c l u t ch engag ed, diesel engine drives a l t e r n a t o r a n d flywheel

control loop with clutch disengaged, diesel engine only

speed feedback

speed governorspeed reference

offset from load sharing module and synchroniser

parameter set 2

parameter set 1

+



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7.5.2 Speed governor systems for redundant UPS's For redundant systems a load sharing module is needed. The function of a load sharing module is to proportional share load between two or more generator sets while the system frequency is held constant. As an accessory to the electronic governor system, the load sharing module measures the active power and continuously controls the governor system. The load sharing module communicates with the other modules in the system either via a analogous paralleling cable or via a serial link, depending of the make and type of the module. Additionally to the load sharing the module provides also the supervision and control functions needed for parallel operation related to the diesel engine. This are reverse power monitoring and ramp generation for loading up generator sets after been synchronised to the common load. Some units do also have a synchronising facility implemented.

7.6 Synchroniser unit The synchroniser ensures that all relevant conditions are established before a circuit breaker is closed. The phase rotation is not always checked from the unit, because it usually can not change after installation and therefore must be checked during the set to work. The synchroniser monitors the beat frequency between two bus bars and tunes one system till zero beat is established. Then a circuit breaker close signal is given. The frequency tuning is done via the speed governor, the control signal can be either an analogous or a digital signal ( lower , higher pulses ) depending of the make and type of the synchroniser. Some synchroniser also perform a voltage matching between the two bus bars, but this feature is not really needed for synchronising the UPS. In case this feature is utilised a control signal is routed to the voltage regulator of the alternator to be synchronised. It also can be either analogous or digital. Some synchroniser offer a voltage supervision function of the differential voltage of the two bus bars, independently from the voltage matching facility. With this units if the differential voltage is greater than a pre-set value no synchronisation is performed.



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8 Supervision and fault handling Depending on kind and importance, faults are divided into different groups which have different effects on the functional sequence of the UPS unit. The Emergency stop fault, which is an exception, is not only routed and displayed by the PLC it also has an external effect (hardware) on all circuit elements of the UPS. The faults mentioned represent the basic faults indications, there may be more faults indications on different units.

8.1.1 Faults causing shut down • Start failure • Oil pressure too low • Over -speed In case one of these faults occurs during diesel engine operation (no mains supply available) the UPS-load circuit breaker is switched off immediately and the diesel engine is stopped. At mains restoration the bypass circuit breaker is instantaneously switched on and the load is supplied by the mains. These faults have no effect during standby operation. The plant operates normally and the fault is displayed by the PLC and/or transmitted through the summary fault output or monitoring system to the control room.

Attention:

In case the fault occurs during standby operation and a mains failure occurs before the fault is cleared, the whole UPS fails and the consumers are no longer supplied.

8.1.2 Faults causing synchronising shut down • Coolant temperature too high • Coolant shortage • Clutch failure • Clutch bearing temperature too high • KIN Module failure • Auxiliaries supply failure When the UPS is in diesel engine operation and mains power returns (within mains switchback delay) and one of these faults occurs, the mains circuit is immediately synchronised, the electromagnetic clutch is disengaged and the diesel engine is stopped. These faults have no effect during standby operation. The plant operates normally and the fault is displayed by the PLC and/or transmitted through the summary fault output or monitoring system to the control room.

Attention:

In case the fault occurs during standby operation and a mains failure occurs before the fault is cleared, the whole UPS fails and the consumers are no longer supplied.



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8.1.3 Bridging retarding faults • Emergency brake • Alternator voltage failure • Alternator bearing temperature too high • Vibration supervision alarm When mains power is supplied and the UPS plant is in standby operation the plant is uninterruptedly switched over to bypass operation in case one of these faults occurs. At the same time the diesel engine is started by high speed start, but no fuel supplied ( fuel valve closed ) and alternator and KIN are braked and stopped due to the compressor load of the diesel engine. In diesel engine operation (no mains power supplied) the consumer circuit breaker , and the ignition of the diesel engine are switched off immediately (clutch remains engaged) and then the UPS is braked until standstill is reached. The bypass circuit breaker is switched on when mains power restores. If there is no mains power supply and the plant is slowing down, the diesel engine is started, speed is adapted, the clutch engaged and the plant is braked until standstill is reached.

8.1.4 Bridging faults causing shut down • Emergency stop • Alternator frequency failure • Alternator over -current • Alternator winding temperature too high • Choke temperature too high If one of these faults occurs the plant is uninterruptedly switched over to bypass operation and stopped. The consumers are directly supplied by the mains. In case no mains power is supplied the bypass circuit breaker is switched on when mains power restores.

8.1.5 Signalling faults • 24V DC power supply failure • Coolant preheating failure • Cooling fan failure • Bypass CB tripped • Synchronising failure • Prelubrication failure • Fuel shortage • Bearing temperature warning • Mains CB tripped • Consumer CB tripped All signalling faults are only signalled and indicated by PLC and do not shut down the UPS.



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8.2 Signalling of faults All fault indications are signalled. A voltage free summary fault output which serves for transmitting the faults to a control room is also activated with every fault. The UPS is also equipped with a horn, which is activated in case of a fault occurrence. The horn is switched off when activating key “Horn off“ or after termination of a pre –set time.

8.3 Maintenance instructions Depending on the number of working hours and/or high speed starts (clutch), maintenance orders are displayed on by the PLC and/or signalled via a separate contact (voltage free) . • Revision of electromagnetic clutch • Grease alternator bearings or check automatic regreaser • Revision of diesel engine After having performed the required task the respective counter has to be reset.

9 Redundant UPS systems In redundant UPS systems two or more UPS sets supply the load. In case one unit fails for any reason the UPS load is still supplied. There are many different arrangements possible. Semantic diagrams of redundant UPS systems.

General requirements for redundant UPS systems Redundant UPS units must be equipped with load sharing modules and prevention must be made for reactive load sharing as well. All other requirements are the same as for single units. The active load sharing has to be ensured by the speed regulating system of the UPS's the reactive load sharing has to be ensured by the alternator's voltage regulating system.

mains input consumer

redundant UPS with individual by - pass circuit breakers for each unit

mains input consumer

redundant UPS with one common by - pass circuit breakers