power distribution in satellite communications

Technical Introduction to Geostationary Satellite Communication Systems Original Prepared by Telesat Canada

Slide Number 1Rev -, July 2001

Vol 4: Earth Stations

Main TVSS

UPS

UP

STV

SS

Provision forFuture Loads

Facilities loads:A/C, lighting, receptacles,

Utility Panel

UPS Panel

Incoming Utility Service 3Ph, 4W

Main Service Panel

Diesel-generatorset

Auto Transfer Switchwith WAMBS

UPS batteries, mountedin the battery cabinet

Main Distribution Panel

Power feeders tocommunication racks

Antenna Deicing(where applicable)

Key-Interlock

Key-Interlock

Power Distribution SystemSection 10



Modern electronic equipment requires a clean, distortion-free supply of Alternating Current (AC).

This type of equipment frequently uses switch-mode power supplies, allowing for the miniaturization of power supply components.

However, switch-mode supplies can have an adverse effect on the quality of the power supplied to other loads.

Therefore, the need for a conditioned power source is clearly apparent when equipment is used in critical applications, where there is no room for failure.


4.10: Power Distribution System

Preamble



Sec 4.10: Power Distribution System

4.10.1: Typical Single-Line Diagram


• A Single-Line Diagram is a simplified schematic of the power distribution system at a given Earth Station.

• A Single-Line Diagram should be prepared in conjunction with detailed engineering diagrams of the AC distribution system.

• It is common practice to post the Single-Line Diagram on the wall near the power distribution switches, making it available for quick reference at times of emergency.

Main TVSS

UPS

UP

STV

SS



Utility Panel

UPS Panel


Main Service Panel

Diesel-generatorset

Auto Transfer Switchwith MBS





WAMBS Key-Interlock

WAMBS Key-Interlock

TYPICAL CONFIGURATION OF POWER DISTRIBUTION SYSTEMFOR A SATELLITE COMMUNICATION GROUND STATION

Figure 4.10.1a. Typical Single-Line Diagram



Main TVSS

UPS

UP

STV

SS



Utility Panel

UPS Panel


Main Service Panel

Diesel-generatorset






WAMBS Key-Interlock

WAMBS Key-Interlock


Part 4.10.1: Typical Single-Line Diagram

4.10.1.1: Redundant Power Sources

Vol 4: Earth Stations, 4.10: Power Distribution System

• The power supplied to the Earth Station from the power utility is often termed “Mains Power” or “Primary Power.”

• The Power System is not fully redundant unless there is a wholly independent backup for Mains Power.

• Most often, the backup power source is a diesel- or gas-fired generator rated at 100% of full station load.

• In remote areas where Mains Power is not available, two generators will be used to provide redundancy.

Figure 4.10.1.1. Typical Single-Line Diagram, Redundant Sources



Main TVSS

UPS

UP

STV

SS



Utility Panel

UPS Panel


Main Service Panel

Diesel-generatorset






WAMBS Key-Interlock

WAMBS Key-Interlock



4.10.1.2: The Automatic Transfer Switch


• The Automatic Transfer Switch (ATS) monitors the quality of Mains Power and, when required, switches all station load to generator power.

• The ATS is tasked with starting and stopping the generator, as required.

• The ATS will be equipped with a Manual Bypass Switch (MBS) so that switchover can be manually accomplished via operator intervention.

Figure 4.10.1.2. Typical Single-Line Diagram, ATS



Main TVSS

UPS

UP

STV

SS



Utility Panel

UPS Panel


Main Service Panel

Diesel-generatorset






WAMBS Key-Interlock

WAMBS Key-Interlock



4.10.1.3: The Main Distribution Panel


• The output of the ATS is made available to all load at the Main Distribution Panel.

• From this point on, there is a functional division between critical and non-critical load.

• Lighting, HVAC (Heating, Ventilation & Air Conditioning), receptacles etc. are usually considered non-essential and are fed directly from the main distribution panel.

• Non-critical load will experience a brief interruption in supplied power when the ATS switches between sources.

Figure 4.10.1.3. Typical Single-Line Diagram, Dist. Panel



Main TVSS

UPS

UP

STV

SS



Utility Panel

UPS Panel


Main Service Panel

Diesel-generatorset






WAMBS Key-Interlock

WAMBS Key-Interlock



4.10.1.4: The Un-interruptible Power Supply


• The Uninterruptible Power Supply (UPS) supplies the Earth Station’s critical technical load with uninterrupted power, even during ATS switchover.

• It does this by providing output AC power via an inverter supplied from a battery bank. The batteries are kept charged by input AC fed to the UPS input from the main distribution panel.

• All electronic equipment directly involved in the provision of service should be considered critical and fed from the output of the UPS.

Figure 4.10.1.4. Typical Single-Line Diagram, UPS



Main TVSS

UPS

UP

STV

SS



Utility Panel

UPS Panel


Main Service Panel

Diesel-generatorset






WAMBS Key-Interlock

WAMBS Key-Interlock



4.10.1.5: Wrap-Around Maintenance Bypass


• Provision must be made for maintenance on the UPS. A Wrap-Around Maintenance Bypass Switch (WAMBS) provides a means of supplying critical load directly from the main distribution panel while the UPS is removed from service.

• The WAMBS is typically inter-locked so that power from one source cannot be removed from critical load before power from the other source is supplied.

• When the UPS is removed from service, critical load is vulnerable to disruption during ATS switchover.

Figure 4.10.1.5. Typical Single-Line Diagram, WAMBS



Main TVSS

UPS

UP

STV

SS



Utility Panel

UPS Panel


Main Service Panel

Diesel-generatorset






WAMBS Key-Interlock

WAMBS Key-Interlock



4.10.1.6: Transient Voltage Surge Suppression


• Transient Voltage Surge Suppressors (TVSS) are recommended on both the main service panel and the UPS distribution panel.

• These devices employ fast-acting components to suppress high-voltage spikes on the line.

Figure 4.10.1.6. Typical Single-Line Diagram, TVSS




4.10.2: Grounding


Grounding is the physical connection between equipment and earth. The earth’s potential is assumed to be zero volts and is used as a reference point.

Bonding is the connection of all electrical and metallic masses in the facility to the same electrical potential. Bonding is part of the Grounding System.

The Grounding System has two primary purposes: safety and power quality.

Definitions




4.10.2: Grounding


Safety Grounding ensures that all non-current carrying metal parts of the electrical system, or metal parts in close proximity to the distribution system, are connected to the same reference point. This ensures the safety of someone touching the metal parts of two pieces of equipment at the same time.

Power Quality Grounding allows all of the equipment to have the same reference voltage. This reduces the possibility of ground-loop currents flowing between units. Ground loop current can damage equipment ports and induce hum into audio and video equipment.

Extensive equipment bonding and grounding is used in modern telecommunication facilities.

Safety & Power Quality



Part 4.10.2: Grounding

4.10.2.1: The Grounding Electrode System


How is it Done?Grounding is usually provided by driving one or more grounding rods—or electrodes—into the earth in the proximity of the Earth Station building.

Resistance & Impedance?The resistance and impedance of the grounding electrode system is very important. Under power distribution system short circuit conditions, the electrodes must divert to ground the high currents present in the system.

Generally, the lower the resistance and impedance the better. Good systems can achieve 2-5 Ohms on average across the grounding system. Acceptable resistance is somewhere between 5 and 10 Ohms

The Grounding Electrode System




4.10.2.2: Enhanced Grounding Systems


Enhanced Grounding SystemsFor sites with very dry soil conditions, a solid rock base, or high soil resistance, it is recommended to consider the installation of a special, chemically enhanced ground electrode system.

Special copper pipes containing conductive electrolytic salts are installed in buried, ground-enhancement materials that surround the pipe, both at the bottom and along the vertical section.

Exothermically welded connection (CADWELD connections) of the grounding cables ensure low impedance and offer the most reliable ground system conductance.



Diesel-generator set

2/0 bare copperHA LO ground

loop inside o f theCom m un ication

Equiupm entRoom

UP S unit

M ain S ervice Panel

A C G round B us

Neutra l

AT S

COMMUNICATIONEQUIPMENT ROOM

C able tray above racks

C om m unica tion Racks (typ ica l)

A/C

Uni

t(ty

pica

l)

G UP S PowerP anel

M ain ACG ro und ing B us

M a in D is tributionP ane l

AC G round B us

Neutra l

HA LOG round ing Bu s

TYPICAL GROUNDING SYSTEM SINGLE LINE DIAGRAM

M ain G roun ding S ystem (bu rried a round the fac ilities)

Figure 4.10.2.4a. Typical Grounding System Single-Line Diagram


4.10.2.4: Grounding System Single-Line Diagram


• A bare copper-conductor loop buried around the building(s) forms the Main Grounding System (MGS). This provides a low impedance path to ground.

• Single point of connection should be used to connect MGS to Main AC Grounding Bus inside the building.

• Main AC Grounding Bus serves as a central connection point for the building grounding systems.

• HALO grounding loops are installed inside the communication room(s).




4.10.2.5: Lightning Protection Grounding


A proper lightning protection system is critical for A proper lightning protection system is critical for any telecommunication facility.any telecommunication facility.

4.10.2.5.1: Key Requirements of a Lightning Protection System• Safely and quickly disperse to ground lightning strike

energy

• Protect humans and equipment from direct and indirect damage

• Reduce the electromagnetic field

4.10.2.5.2: Typical configuration of the Lightning Protection System• Only one connection point between interior and exterior

systems

• Low impedance to ground of the exterior system




4.10.2.5: Lightening Protection Grounding


A proper lightning protection system is critical for A proper lightning protection system is critical for any telecommunication facility.any telecommunication facility.

4.10.2.5.3: Transient Voltage Surge Suppressors• Fast-acting devices to rapidly shut lightning surges to

ground

• Installed at the main power service entry point and at points along the power distribution system

• Must have a very fast response time and high energy-dissipation capacity

• A good ground connection is essential



Part 4.10.3: Factors Affecting Power Quality

4.10.3.1: Power Outage

Power Outages can be in the form of complete interruptions of voltage on one or more phases of the supply line.

Voltage drops to less than 80% of nominal value for more than 2 seconds are also considered power outages.

In the absence of appropriate power protection, a power outage condition will result in complete interruption of operation, possible damage of components, and possible corruption or loss of electronic files.

Power Outages





4.10.3.2: Undervoltage and Overvoltage

An undervoltage condition is one in which the voltage on one or more phases of the incoming supply drops to between 15% and 20% of nominal for more than 2 seconds. Voltage drops beyond 20% are considered power outages.

Undervoltage


OvervoltageAn overvoltage condition is one in which the voltage on one or more phases of the incoming supply increases to 10% or more of nominal for more than 2 seconds.

AffectUnder- or Over-voltage conditions can result in damage to electronic equipment, excessive currents, or overheating and burning of input transformers.




4.10.3.3: Frequency Variation

Frequency is typically the most stable parameter of the power supply grid.

However, switching of the utility grid may result in momentary frequency change.

Operation of the ground station from the local emergency diesel-generator set can expose critical loads to unstable frequency performance.

Poor frequency control can result in damage to electronic equipment, overheating, fast or slow running clocks, and the burnout of motor coils.

Frequency Variation





4.10.3.4: Sags and Swells

Sags and Swells are, respectively, under- and over-voltage conditions which last less than 2 seconds.

These events are typically caused by large loads being added or removed from the power grid.

Automatic Transfer Switches are usually not set to switch to their associated generators on Sags and Swells.

Sags and Swells cause nuisance interruptions of operation of equipment that is not on protected power.

Sags and Swells





4.10.3.5: Transients and Noise

Transients are high frequency spikes of 1 to 100 times normal amplitude travelling in the power distribution system and lasting only nanoseconds.

Transients


Electrical noise is a distortion of the normal power supply sine wave.

Normal-mode noise is the voltage noise that always exists between a pair of conductors. In a typical 3 phase distribution system it is a voltage appearing equally in phase with each line-to-ground voltage.

Common-mode noise appears between the neutral conductor and the grounding conductor (ground).

Noise




4.10.3.6: Harmonics

Harmonics are frequency distortions of the fundamental frequency supplied from the power grid (60 or 50 Hz).

Harmonics are typically caused by the superimposition of other, higher frequencies generated by loads that draw current in abrupt pulses rather than steadily, such as switched-mode power supplies.

Harmonics can cause a “flattening” at the peaks of the 60 or 50 Hz sine- wave, reducing the RMS value of the voltage.

Harmonics can cause both nuisance and permanent equipment damage.

Harmonics





4.10.4: Emergency Power Systems


DefinitionThe Definition of Emergency Power System as ratified by the Institute of Electrical and Electronic Engineers (IEEE) is as follows:

“An independent reserve source of electric energy which, upon failure or outage of the normal source, automatically provides reliable electric power within a specified time to critical devices and equipment whose failure to operate satisfactorily would jeopardize the health and safety of personnel or result in damage to property”



Part 4.10.4: Emergency Power Systems

4.10.4.1: Power System Redundancy


To greatly improve the availability of the communication links handled from any Earth Station, the installation of a redundant source of electrical power is highly recommended.

This redundant source should be available immediately upon the failure of the normal power supply.

Availability

• One or more diesel generator sets.

• One or more UPS.

• One or more additional feeds from the utility grid.

Forms of Redundancy




4.10.4.2: The Diesel-Generator Set


Diesel generator sets—or gensets—are rated in kilovolt-amps (kVA). They are usually sized to support 100% of station load.

The genset rating must also be coordinated with the size of the UPS. Typically, the genset ought to be able to provide 160% of the nominal UPS rating, plus any additional station load.

The genset rating should take into account any future plans for expansion.

4.10.4.2.1: Capacity and Rating






The required backup time at full load, as well as refueling method and availability, are determining factors in fuel tank sizing.

Environmental considerations and local building/environment codes also play a part in the fuel tank sizing decision.

When fuel is stored on site, consideration must be given to proper containment and cleanup in the event of a spill.

4.10.4.2.2: Fuel Tank Capacity






The diesel generator is ordinarily not running unless required, and must be started when backup power is desired. Consequently, start batteries and a battery charger are needed.

Batteries should be heavy-duty, lead acid type, and should be collocated with the generator. Frequent inspections are required.

The battery charger must be a good quality, float voltage type, with the capability for remote monitoring.

4.10.4.2.3: Battery Charger and Batteries

Each component in the Emergency Power System must provide for remote monitoring.

4.10.4.2.4: Monitoring




4.10.4.3: The Automatic Transfer Switch


The Automatic Transfer Switch monitors power condition and controls transfer of the source of supply from Normal to Emergency power, and re-transfer to Normal.

Provision of a switchable neutral is recommended to ensure a neutral ground at the generator set.

Features like Automatic Diesel Start, Time Delay on Start, Time Delay on Re-transfer, Diesel Cool-down should be built into the ATS. Frequently, the battery charger is installed inside the ATS enclosure.

The Automatic Transfer Switch

Figure 4.10.4.3. ATS

Photo Courtesy of Telesat Canada

A set of dry contacts for remote monitoring of the ATS is required. These contacts should be extended to central monitoring and control system.




4.10.4.4: The UPS System


An Uninterruptible Power Supply is a device that immediately substitutes battery power for AC power when the AC is lost. The load being served by the UPS does not experience any loss of power.

Thus, a UPS provides isolation of technical loads from the unstable utility grid. This is the primary purpose of the UPS system.

In the event of an ATS switchover, which can take several seconds, the UPS provides battery power to the technical load so that power continuity is assured.

The UPS system also filters voltage and frequency disturbances on the supply line, producing clean, uninterruptible output power to support critical technical loads.

4.10.4.4.1: The Importance of UPS Power






Main UPS topology configurations: • Online • Offline

• Line-Interactive and • Standby

Online type UPS systems: during Normal operation, the main power path is through the rectifier and inverter sections (double conversion), from inverter and batteries during power failure and through the Bypass line in case of internal UPS failure.

Offline type UPS systems: the main power path is through the input filtration and surge suppression section, directly to the load. During input power failure, the UPS unit activates the inverter and delivers the output power from the batteries through the inverter.

4.10.4.4.2: Available Configurations



Battery

ACDC AC

DC

Bypass Line

AC Input

AC Output

Static SwitchRectifier Inverter

Double conversion On-Line UPS System configuration

Normal Operation

Emergency Operation

Figure 4.10.4.4.2.1. Online UPS Configuration





The Online configuration is the most popular arrangement for UPS systems.

4.10

.4.4

.2.1

On

line



Figure 4.10.4.4.2.2. Line-Interactive UPS Configuration





A good compromise for small facilities.

4.10

.4.4

.2.2

Of

fline

Lin

e-In

terac

tive

Battery

ACDC

AC Input

AC Output

Transfer Switch

Bi-directional Rectifier/Inverter

Line Interactive UPS System configuration

Charging (normal conditions) Discharging (power failure conditions)

Normal OperationEmergency Operation



Figure 4.10.4.4.2.3. Offline UPS Configuration





A low-cost, high efficiency choice.

4.10

.4.4

.2.3

Of

fline

Stan

dby

Battery

AC Input AC Output

Transfer Switch

Off-Line UPS System configuration

ACDCDCACSmall

Charger


Inverter



4.10.4.4.3: Capacity




The electrical capacity of a UPS system should, as a minimum, meet the following design criteria:

• Sufficient capacity for all estimated station technical load.

• Provide spare capacity for future expansion (optional).

• Ensure that the UPS system is rated to support technical loads with a high content of switch-mode input power supplies (crest factor of at least 3:1).

• Provide 20% overhead (i.e. full anticipated UPS load should not exceed 80% of its nominal kVA rating).



4.10.4.4.4: External WAMBS




As with any other electrical equipment, the UPS system is not immune to catastrophic failure.

Such a failure might totally cut off power supply to critical loads.

Installation of an alternative external bypass power path that can be manually selected via a Wrap-Around Maintenance Bypass Switch (WAMBS) is strongly recommended.

This will allow total isolation of the failed UPS system so that the UPS can be replaced and fully tested prior to the reconnection of load. Figure 4.10.4.4.4a. WAMBS

Photo Courtesy of Telesat Canada



4.10.4.4.4: External WAMBS - Simplified Diagram




Figure 4.10.4.4.4b. WAMBS Diagram

AC Output to Critical Load


Battery

UPS UnitUPS Unit

Circuit breakers interlock

External WAMBS

Power panel

Input

External Bypass



4.10.4.4.5: Batteries




UPS battery backup power is provided by banks of 10’s to 100’s of batteries.

The size of the battery system depends on the size of the load that must be supported and the desired maximum support time.

Valve Regulated Lead-Acid (VRLA) batteries are typically installed directly inside small and mid-sized UPS units.

Large UPS systems use wet cell, lead-acid batteries. These will be installed in a separate, well ventilated room.

Float-type battery chargers will be used to maintain the charge on all batteries.



4.10.4.4.5: Batteries - Temperature Compensation Curve




Temperature compensation is required for charging voltages.

Degrees C

Vol

ts p

er c

ell

2.15

2.25

2.35

10 C0 30 C20 C 40 C 50 C

Optimum operating conditions

Temperature coefficient

Figure 4.10.4.4.5. Temperature Compensation Curve



4.10.4.4.6: UPS Monitoring




A comprehensive monitoring system is recommended for UPS systems.

Each UPS unit should have a set of dry contacts or an RS232 (or equivalent) port for remote monitoring of the status of the unit.

At minimum, the unit’s summary alarm status should be tied into the station’s Monitor and Control (MAC) system to alert operators of presence of alarms on the system.

As a minimum, the summary alarm status should include “UPS on batteries”, “UPS on By-pass”, “Trouble” and “Low battery voltage”.



In sizing the UPS for a site, it is handy to have a rough idea of the power requirements of typical satellite communication equipment. Summary of typical loads

Equipment Estimated Load (VA)1.5 kW Klystron 11,500

400W TWTA 2,90040 SSPA 370

Up-converter 110Down converter 110

Modem 70


4.10.4.5: Typical Electronic Device Power Consumption


Typical Power Consumption

power distribution in satellite communications

Engineering