TES-P-103-06R0

TRANSMISSION ENGINEERING STANDARD

TES-P-103.06, Rev. 0

TABLE OF CONTENTS

1.0

PURPOSE AND SCOPE

2.0

DC POWER SYSTEM CONFIGURATION

3.0

ENVIRONMENTAL

4.0

COMPONENTS OF COMMUNICATION DC POWER SYSTEM 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9

48V Battery Bank with Rack or Cabinet Battery Chargers Tie Box or Interconnection Box DC Distribution, Metering and low voltage Disconnect Unit AC Distribution Panel Battery Disconnect Switch Static Inverter with Static Transfer Switch System Interconnection wiring/cabling Communication System Grounding

FIGURE 1:

Scheme CX1 Telecom DC Power Supply System – Interconnection Diagram for Office Building with SCR OR Ferro-resonant or Saturable Reactor Charger.

FIGURE 2:

Scheme CX2 Telecom DC Power Supply System – Interconnection Diagram for Office Buildings with Modular Type Switched Mode Chargers

FIGURE 3:

Scheme CX3 Telecom DC Power Supply System – Interconnection Diagram for Power Plants and Substations with SCR OR Ferro-resonant or Saturable Reactor Charger.

FIGURE 4:

Tie Box or Interconnection box for Telecom DC Power Supply System

FIGURE 5:

DC Distribution Metering & Low voltage Disconnect Panel

TESP10306R0/AMM

Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

1.0

2.0

TES-P-103.06, Rev. 0

PURPOSE AND SCOPE 1.1

This Standard covers the design requirements for (-) 48V DC (Positive Ground), Telecommunication grade, DC Power System supporting Fiber Optics equipment, PABX and radio equipment in the SEC Office Building, Power Plants and Substation. The DC Power System output voltage range shall be from -42V to -56V DC unless otherwise specified.

1.2

This standard does not cover the following: 1.2.1

Substation DC power systems

1.2.2

Communication power systems that are driven from propane fueled thermal electric generators (TEG)

1.2.3

Communication power systems powered by solar modular photovoltaic power supplies.

DC POWER SYSTEM CONFIGURATION

2.1

2.2

The DC Power System shall generally comprise the following equipment: •

48V Battery bank with rack or cabinet.

•

Communication grade rectifier chargers.

•

Tie Box or Interconnection Box.

•

DC Distribution, Metering and low Volts Disconnect Unit

•

AC Distribution Panel

•

Load Break Battery Disconnect Switch

•

Step down transformer required if 127V single phase supply is not available in AC panel board.

•

Communication grade Static Inverter and Static Transfer Switch (This is optional equipment. It is required when the Telecommunications load includes PABX associated Computers, Monitors and Modems)

•

System Interconnection Wiring/Cabling

•

System Grounding

DC power system in office buildings shall consist of either three Silicon Controlled Rectifier (SCR) type, or Three Ferro-resonant (FR) type chargers or Three

TESP10306R0/AMM

Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

TES-P-103.06, Rev. 0

Saturable Reactor (SR) type chargers each rated for 50% capacity of the DC system load (on load sharing basis) and the rest of the components/Systems listed in clause 2.1 (Refer Scheme CXI, Figure 1). Alternatively the system shall consist of 'N+l' equally sized modular type Switched mode chargers ('N' of which are adequate to carry totally the DC system load) and the rest of the components/Systems listed in paragraph 2.1, except the tie box (Refer Scheme CX2, Figure 2). Switched mode type chargers and hence scheme CX2 shall be preferred to all extent possible. 2.3

DC power system in power plants or substations shall consist of two SCR, or two ferro-resonant or two Saturable Reactor (SR) type chargers each rated for 100% capacity of the DC system load and the rest of the components/systems listed in Clause 2.1 (Refer Scheme CX3, Figure 3). The inverter and static transfer switch however is required only when the Telecommunication load includes PABX associated Computers, Monitors and Modems.

2.4

For schemes CXI & CX3, the battery chargers shall be floor or wall mounted as specified in data schedule for the battery charger. The fused battery disconnect and the AC panel board shall be wall mounted. For scheme CX2 all components except the AC panel board, the fused battery disconnect and battery bank shall be mounted on a 483 mm or 584 mm relay rack.

3.0

ENVIRONMENTAL All AC and DC power equipment listed in clause 2.1 shall be installed indoor in airconditioned rooms. Room temperature and other conditions to be considered for the communication power system design shall be as stated in 01-TMSS-01.

4.0

COMPONENTS OF COMMUNICATION DC POWER SYSTEM 4.1

48V Battery Bank with Rack or Cabinet 4.1.1 The type of batteries, whether vented type lead acid or VRLA type sealed or nickel cadmium type shall be based on criterion given in TES-P-103.02. The batteries shall meet the requirements of 46-TMSS-01 for vented type lead acid batteries or 46-TMSS-04 for VRLA batteries or 46-TMSS-06 for Nickel Cadmium batteries as applicable. 4.1.2

Cell selection criteria shall be based on TES-P-103.02, 46-TMSS-01 and 46TMSS-06 as applicable.

4.1.3

The layout of battery room and racks shall be based on the criteria given in TES- P-103.04.

4.1.4

The sizing of the communication battery shall be based on the following Guidelines:

TESP10306R0/AMM

Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

TESP10306R0/AMM

TES-P-103.06, Rev. 0

a.

Based on the voltage window of -42 to -56 V as specified in Clause 1.1 and lead acid battery with float charging voltage of 2.2 V per cell , SEC has standardized 24 battery cells connected in series for 48V nominal DC system.

b.

The number of cells for nickel cadmium battery shall be calculated on case to case basis of nominal and permissible minimum and maximum DC system voltages and in the light of self discharge and charging time as limiting factor, which may result in using larger cell that would otherwise have been necessary (Refer IEEE 1115). Based on the minimum DC system voltage of -42V and minimum end voltage 1.1 V of the cell, SEC has standardized 39 cells for 48 V nominal DC system voltage. Dropping diodes may be used in the circuit to avoid over voltage beyond permissible limits as indicated in 46-TMSS-05.

c.

For DC system voltage other than 48V, the no. of cells shall be calculated per IEEE 1115 for Nickel-Cadmium batteries and per IEEE 485 for lead acid batteries.

d.

Each cell of the battery bank shall be designed for 100% AH ratings. Parallel connection of cells to achieve the desired AH rating is not acceptable.

e.

The final end of the discharge voltage shall be 1.75 volts per cell for lead acid cells and 1.1 V per cell for Ni-Cad cells irrespective of the battery application, whether it is for central office or buildings or power plants and substations. However manufacturers recommended value of minimum end of discharge voltage shall be cross checked and the values specified shall not be lower than those recommended by the manufacturer.

f.

The battery shall be designed to feed the communication DC system load for a back-up time duration of 8 hours for central office/office building and 12 hours for power plants or substations.

g.

The duty cycle of communication batteries is continuous unlike substation batteries with multi-stepped duty cycle. The sizes of the battery bank need to be reconfirmed for individual project based on actual duty cycle and load requirements on the guidelines specified in TES-P-103.02.

h.

The battery shall be designed to cater to the maximum telecommunication load. Only for Telecommunication Power System represented by Figure 2 (Scheme CX2), this should include provision for future expansion of the Telecommunication system. Unless otherwise specified, future addition of load may be assumed as 50% of the present load for this purpose.

Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

i.

TES-P-103.06, Rev. 0

The following formula shall be used for determining the battery capacity: AH = L × H × K d × K TI × K A Where:

4.2

AH

=

Required ampere-hour capacity (C8 when 'H' is 8 hours and C12 when 'H' is 12 hours)

L

=

Maximum continuous Telecommunication System DC load in amperes (Equal to DC watts/ 48V x efficiency) Efficiency value to be assumed as 0.9.

H

=

Back up time duration in hours

Kd

=

Design margin factor which shall be taken as 1.1.

KTI

=

Temperature Correction Factor. Though for airconditioned room with temperature maintained at 25 ºC, this factor would have been 1, a temperature correction factor of 1.19 based on inside room temperature of 10 ºC consequent to AC power failure in winter season shall be used. Temperature correction factor for Nickel Cadmium cells shall be as per TES-P-103.02.

KA

=

Ageing factor of 1.25. This Factor shall not apply to battery banks of plante type plates of pure lead as it is expected that no ageing takes in place in plante design.

Battery chargers 4.2.1

4.2.2 TESP10306R0/AMM

Unless otherwise specified, as a general accepted SEC viewpoint, the type of chargers to be selected shall be as follows: a.

For power plants and substations, the type of chargers shall be silicone controlled rectifier (SCR) type or ferro-resonant (FR) type or Saturable Reactor (SR) type as specified in the project document.

b.

For central offices and office buildings switched mode type of chargers shall be preferred to SCR, FR or SR type chargers unless there are there other compelling reasons.

The chargers shall meet the requirements of 46-TMSS-05. All alarm contacts provided for remote annunciation shall be wired to the Main Distribution Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

TES-P-103.06, Rev. 0

Frame (MDF) for connection to the surveillance system in the SEC Control Center. 4.2.3

The sizing of the battery chargers shall be based on the following guidelines: a.

b.

The charger output DC voltage range shall be selected considering the following: •

Float charge voltage of the battery bank

•

Equalize/boost charge voltage of the battery bank

•

Commissioning charge voltage of the battery bank during initial first charge of the battery bank. (Load shall not be connected to the DC system during this operation).

•

The DC load voltage shall not operate outside the limits of 42-56 volts during float/equalize or boost charging operations.

The charger output DC current rating shall be selected using the following formula: ⎛ BIF × AHR ⎞ ⎟⎟ × CF A R = ⎜⎜ SF × L + RT ⎠ ⎝

Where:

TESP10306R0/AMM

AR

=

Output ampere rating of the charger

SF

=

Service factor of 1.1

L

=

Total continuous DC load in amps of the communication system

BIF

=

Battery Inefficiency Factor shall be as recommended by the manufacturer or 1.1 whichever is more.

AHR =

Battery ampere-hour based on 8 H or 12 H rating as applicable.

RT

Battery recharge time in hours to recharge the battery from fully discharged condition to 90% of its rated ampere hour capacity. For substations and power plants this shall be taken as 8 hours and recharging time to 100% capacity shall not exceed 16 hours. For office

=

Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

TES-P-103.06, Rev. 0

buildings this shall be taken as 16 hours and the battery shall be 100% recharged in 24 hours. CF

=

Configuration or capacity factor which is a function of charger configuration or percentage charger capacity (Refer to clause 2). The value of this factor shall be as follows: 0.5

1.0

1 N

For 3 Nos. or 2 Nos 50% capacity chargers in parallel (Refer to clause 2.2). For 2 Nos. 100% capacity chargers in parallel (Refer to Clause 2.3).

For ‘N+1’ chargers of 100/N% capacity in parallel (Refer to clause 2.2).

c.

4.3

Adequate space and wirings shall be provided in the 483 mm or 584 mm rack for DC system represented by Figure 2 (Scheme CX2) to cater for future expansion in Telecommunication load up to 50%. The number of additional chargers required for this future expansion shall be worked out to maintain the same idea that “N” chargers will be adequate to meet the ultimate load.

Tie Box or Interconnection Box The Tie Box shall be as per Figure- 4 and shall consist of Positive and Negative Bus bars with terminals for the termination of the Battery Charger Leads, the Battery Leads and input leads of the DC Distribution, Metering and Low Volts Disconnect Panel. The Tie Box shall be rated for 65 V DC and the bus bars shall be designed for 3 seconds withstand of battery short circuit current plus the available short circuit current from all the chargers connected. Provision for Connecting three minimum DC Distribution Metering and Low Volts Disconnect Panels shall be made. A shunt, compatible with the battery ammeter located on the DC distribution, Metering and Low Voltage Disconnect shall be provided. The shunt leads to the ammeter shall be terminated on a terminal block. The Tie Box shall be wall mounted and be fabricated with a welded sheet steel material. The degree of Protection shall be IP21 per IEC 60529.

4.4

DC Distribution, Metering and Low Voltage Disconnect Unit 4.4.1 The unit shall be rated for 65V DC operation and shall be designed for 3 seconds withstand of battery short circuit current plus the available short circuit current from all the chargers connected. The unit shall be wall mounted for schemes CX1 and CX3 and panel mounted for scheme CX2. Wall mounted units shall be fabricated with a welded sheet steel material with degree of protection IP21 per IEC 60529. The unit shall comprise of:

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Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

a.

TES-P-103.06, Rev. 0

Wall mounted units (Scheme CX1 & CX3), positive and negative busbars for termination of the Input Positive and Negative wires from the Tie Box. The Positive Bus Bar shall be provided with terminals for Branch Load Circuits. Alternatively a separate Positive busbar with terminals shall be provided for the Branch Load Circuits. The first set of bus bars shall be rated for the total current output of 2 Nos. 50% chargers or 1 No. 100% charger depending upon the configuration adopted plus 25%. The positive load bus bar if provided shall be rated for maximum communication DC system load current plus 25%. For panel mounted units (Scheme CX2) Positive and Negative Bus bars shall be manufacturer’s standard design. One positive bus bar with terminals for each breaker position shall be provided for each panel.

b.

Outgoing circuits shall be protected with single pole or double pole circuit breakers. The number of outgoing circuits shall be based on the number of actual circuits required for the project plus 20% spare for Scheme CX1 and CX3. For Scheme CX2, initially a total of 20% spare shall be provided. Provision shall be made for installing 30% additional breakers to cater to future expansion in the telecommunications load.

c.

One DC load voltmeter 0-75V range (2% accuracy analog of 89 mm or digital of 3 digits).

d.

One DC load ammeter with associated shunt (range of ammeter shall be based on maximum communication system DC load plus 50 % extra with due considerations given to any high inrush current load. The meter shall be of 2% accuracy analog of 89 mm or digital of 3 digits).

e.

Low Voltage Disconnect (LVD) feature to disconnect the load at adjustable voltage setting of (-) 42 to (-) 48 VDC (to be set at (-) 42V (unless otherwise specified) during the battery discharge. The LVD shall reset on return of healthy voltage on its terminals and reconnect the load back to the DC system at (-) 51V. The LVD shall be rated to a current same as the positive load bus bar rating.

4.4.2 Each of the circuit breakers referred in paragraph 4.4.1 above shall have identification label and shall:

TESP10306R0/AMM

a.

Be of DC interrupting rating same as or better than the short circuit current value specified for the panel in paragraph 4.4.1 above.

b.

Be provided with thermo-magnetic releases. In case of loads with high inrush currents, the release shall be slow acting. Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

c.

TES-P-103.06, Rev. 0

Be provided with form ‘C’ trip/off auxiliary contacts. The auxiliary contacts shall be wired to provide visual group alarm (Red LED) on the panel and also provide a set of potentially free form “C” contact. The form ‘C’ contacts shall be wired to the Main Distribution Frame (MDF) for onward connection to the surveillance system in the respective SEC Control Center.

4.4.3 A DC Ammeter compatible with the shunt located in the tie box shall be provided to measure the charge/discharge current of the battery. The meter shall be as per 40-TMSS-01 and analog of 89 mm or digital of 3 digits. The range of the meter shall be adequate to cover the maximum discharge and charge current permitted for the battery including test discharge current. The leads of the Ammeter shall be terminated on a terminal block. 4.5

AC Distribution Panel 4.5.1 The panel shall be rated for the low voltage distribution AC voltage available at the installation (The voltage available at the site will be indicated by the Project Engineer in the Scope of Work and Technical Specifications for the project). The panel shall comprise of: a.

The bus bars rated for the total AC input current to 2 Nos. 50% chargers or 1 No. 100% charger or (‘N’) chargers depending upon the configuration adopted for communication DC system plus 50% for future load additions. The short circuit rating shall be for minimum one second for the short circuit current of the AC system on the incoming side of the panel.

b.

One, ‘Three pole’ with neutral or “2 pole” (2 lines) with neutral incoming circuit breaker of continuous current capacity same as the bus bars in paragraph 4.5.1.(a).

c.

Number of outgoing triple pole, two pole or single pole circuit breakers for charger circuits depending upon the type of chargers as follows: For SCR, FR and SR type chargers: • One circuit breaker separately for each charger • One spare circuit breaker And for Switched Mode type chargers: • One common circuit breaker for ‘N+1’ chargers • One spare circuit breaker

d. TESP10306R0/AMM

One, outgoing, circuit breaker for the bypass input, if a static transfer switch is installed. The circuit breaker shall be single pole or double Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

TES-P-103.06, Rev. 0

pole depending on the AC voltage available in the AC Distribution panel. e.

One spare circuit breaker of same rating as 4.5.1. (d) above.

4.5.2 The circuit breakers referred in paragraph 4.5.1 above shall:

4.6

a.

Be of minimum interrupting rating equal to or greater than the short circuit level of the AC system on the incoming side of the panel.

b.

Be provided with thermo-magnetic release with incomer release provided with time delay to coordinate with the outgoing breaker instantaneous short circuit release.

Battery Disconnect Switch The battery disconnect switch shall: 4.6.1 Be of double pole, load break type designed for carrying and breaking successfully the maximum DC current (charge or discharge) flowing in the battery circuit. 4.6.2 Be provided with fuses capable of interrupting the maximum DC short circuit current. 4.6.3 Be provided with dry (voltage free) form ‘C” contact separately for the disconnect switch and fuses to give alarm on the Main Distribution Frame (MDF) whenever the disconnect switch opens and also whenever the fuses blow. 4.6.4 Be housed in an IP21 per IEC 60529 type enclosure. Padlock with key shall be provided to padlock the operating handle of the disconnect switch. 4.6.5 Be located close to the door, but outside the battery room (wall mounted) when battery bank is located inside a dedicated battery room. When VRLA batteries are installed along with other telecommunication equipment in a common room, the disconnect switch may be mounted on the DC panel or wall mounted close to the battery bank.

4.7

Static Inverter with Static Transfer Switch: 4.7.1 When specified, communication grade, static inverter with static transfer switch shall be provided to give uninterruptible AC power supply to Personal Computers (PCs), monitors and modems associated with PABXs. In order to keep the inverter and hence the battery and charger sizes low, the output of the inverter for typical telecommunication application in SEC shall be limited to one (1) kVA and the only loads to be connected to inverter

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Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

TES-P-103.06, Rev. 0

(through the static transfer switch) shall be the following, unless otherwise specified. a. b. c.

2 Nos. Personal Computers 2 Nos. Monitors 1 No. Modem

The inverter system shall be sized to cater to the maximum load plus 25% margin to cater to any unforeseen requirements and/or for future loads. 4.7.2 The static transfer switch shall operate in the reverse mode as follows: a.

Under normal conditions, the load shall be connected to the inverter.

b.

On failure of the inverter, the transfer switch shall transfer the load to the ‘alternate’ or ‘by-pass’ mode controlled by a dedicated AC circuit breaker as mentioned in paragraph 4.5.1(d).

4.7.3 The static transfer switch rating shall be selected to match the output of the inverter. 4.7.4 The entire system shall generally meet the requirements of applicable clauses of 46-TMSS-03 and TES-P-103.05 for UPS system. 4.8

System Interconnection Wiring/Cabling: The wiring/cabling between the various equipment of the communication power supply system shall: 4.8.1 Be based on figures No.1, No.2, No 3 and No.5 as applicable and the layout of various equipment in the communication room. 4.8.2 Be such as to limit the voltage drop to within 0.5V DC in the power cables from: a.

Battery to load considering that the battery is discharging at maximum design discharge current.

b.

Charger to load considering that the charger is supplying the maximum battery charging current and the rated/design load current.

4.8.3 Be such that twin core cables or single core cables shall be used for DC power circuits. When single core cables are used, conductors of opposite polarity belonging to the same circuit should be run close to each other so that the magnetic fluxes from current moving in opposite directions cancel out each other. 4.8.4

TESP10306R0/AMM

Be run in rigid electrical metallic conduit (EMT) complying with the latest edition of NEC or on metallic cable trays. All AC wirings must be run in Date of Approval: October 9, 2007

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TRANSMISSION ENGINEERING STANDARD

TES-P-103.06, Rev. 0

rigid electrical metallic conduit. Also, main DC wiring from the rectifier enclosure to the DC panel board shall be run in rigid electrical metallic conduits. For office buildings approved non-metallic cable trays/raceways are permitted for power cables. 4.8.5 Be with color code of red for ungrounded DC negative wire, black for the grounded positive wires and green or green with yellow stripes for ground wires. For AC wiring, color coding shall conform to NEC. 4.9

Communication System Grounding The grounding system shall consist of wiring, buses (GWB- ground window bar and MGB-master ground busbars), connectors and connections that resist deterioration and require minimal maintenance. The positive of the battery shall be grounded through GWB in the telecommunication room to the MGB. The communication grounding system shall generally conform to TES-T-111.02.

TESP10306R0/AMM

Date of Approval: October 9, 2007

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Date of Approval: October 9, 2007

TES-P-103.06, Rev. 0

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Figure 2: SCHEME: CX2

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Date of Approval: October 9, 2007

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Figure 3: SCHEME: CX3 DWG # TE-0306-0300-00

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Date of Approval: October 9, 2007

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Date of Approval: October 9, 2007

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Date of Approval: October 9, 2007

TES-P-103.06, Rev. 0

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