Transformer Specifications

Power transformers are used throughout the Electrical Industry, Electrical Utilities, Oil and Gas, and many others use transformers to, step up voltage for transmission or step-down voltage for distribution.

A HV Power transformer is one of the more complicated machinery in the electrical industry. Transformer Design therefore is complex and needs special knowledge to design correctly.

The design of the transformer is in two stages as follows:

• First - Internal design – this is the responsibility of the transformer manufacturer. Following a client’s specifications, the manufacturer builds the transformer accordingly.
• Second - Installation design – this is the responsibility of the client once the transformer is manufactured and delivered.

EDM program focuses on the Installation design, such as the selecting the Transformer internal current transformer parameters , selecting and wiring the alarms, trips and control of the auxiliary devices associated with the transformer.

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Transformer Tables:

Secondary MVA Selection Table

Tertiary MVA Selection Table

Internal Current Transformer Selections

The Current Transformer ( C.T. ), is a type of “instrument transformer” that is designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an AC transmission line using a Guidelines for ammeter. The principal of operation of a basic current transformer is slightly different from that of an ordinary voltage transformer.

There are a variety of metering applications and uses for current transformers such as with wattmeter’s, power factor meters, watt-hour meters, protective relays, or as trip coils in magnetic circuit breakers, or MCB’s.

Current transformers can reduce or “step-down” current levels from thousands of amperes down to a Guidelines for output of a known ratio to either 5 Amps or 1 Amp for normal operation. Thus, small and accurate instruments and control devices can be used with CT’s because they are insulated away from any high-voltage power lines.

EDM assumes current transformers have a Guidelines for secondary rating of 5 amps with the primary and secondary currents being expressed as a ratio such as 100/5. This means that the primary current is 20 times greater than the secondary current so when 100 amps is flowing in the primary conductor it will result in 5 amps flowing in the secondary winding.

Current Transformer Configuration Table

Primary

Secondary

Tertiary

Current Transformers Summaries

Internal CT#	CT Function	Ratio	Connection
Make Selection 1 2 3 4	Make Selection ETM AVR		X1-X2

Transformer Alarms, Trips, and Controls

Transformers are the most expensive piece of apparatus in a power substation and therefore must have appropriate protection equipment installed to guard against various faults.

EDM organizes alarms and trips from internal transformer faults and follows through with a complete design including schematics and wiring diagrams and cabling.

In order to react properly in faulty situations it’s important for designers to understand how internal protection mechanisms of a transformer work.

EDM provides additional information on alarms and trips because of the importance of understanding what is going on inside a transformer when under fault conditions and why.

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Transformer Trips

Additional Transformer Trips

Transformer Protective Relay Alarms

Transformer Protective Relay Trip

Additional Transformer Protective Relay Trips

Transformer Control Alarms

Additional Transformer Control Alarms

Transformer Tap Changer (Oil Emersed) Alarms and Trips Summary

Transformers are the most expensive piece of apparatus in a power substation and therefore must have appropriate protection equipment installed to guard against various faults.

EDM organizes alarms and trips from internal transformer faults and follows through with a complete design including schematics and wiring diagrams and cabling.

In order to react properly in faulty situations it’s important for designers to understand how internal protection mechanisms of a transformer work.

EDM provides additional information on alarms and trips because of the importance of understanding what is going on inside a transformer when under fault conditions and why.

Note: The hashtag (#) symbol on a cell title indicates additional information is available, access it by clicking on the hashtag.

Tap Changer Alarms

Tap Changer Trips

Additional Tap Changer Trips

Copper and aluminum are the two major conductor materials used for substation buses and equipment connections. Both materials can be fabricated into various types of flexible or rigid conductors. The trend in substation construction is toward use of mostly aluminum conductors. Copper conductors are used principally for expansion of similar systems in existing substations.

The conductivity of aluminum is from 50 to 60 percent that of copper, depending on the aluminum alloy. Consequently, larger aluminum conductors are required to carry the same currents as copper conductors. The larger aluminum conductor diameters result in greater wind and ice loads but tend to minimize corona, which is more of a problem at higher voltages.

For the same ampacity, copper conductors weigh approximately twice as much as aluminum conductors. The higher copper conductor weights can result in more sag as compared with aluminum conductors for equal spans. To reduce the sag, it is usually necessary to increase the number of supports for rigid conductors or, in the case of flexible conductors, increase the tensions.

Aluminum conductors are available in a variety of alloys and tempers with different conductor conductivities and strengths. Round tubular conductors are usually specified as either 6061-T6 or 6063-T6 alloy. The 6063-T6 alloy has a conductivity approximately 23 percent higher and a minimum yield strength approximately 29 percent lower than the 6061-T6 alloy. Consequently, the 6063-T6 alloy can carry higher currents but may require shorter support intervals. Both Schedule 40 and 80 pipe are available in either alloy. The Schedule 80 sizes have wall thicknesses approximately 40 percent thicker than the Schedule 40 sizes, resulting in lower deflections for equal span lengths.

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Transformer CAD/Export Generator

All transformer drawings, from Transformer Single Lines, AC and DC Schematics, to Wiring Diagrams, can be generated from here!

Title Block Information

HV Transformer Reference Library

Control Cable Specifications

Control cables are used to connect instrument transformers, coils of circuit breakers and contactors, control switches, meters, protection devices and other control and monitoring equipment. Control cables have conductors in copper, insulation and outer sheath in PVC and they may have up to 150 cores.

Control cables are mainly used for Equipment control purposes. Each core is identified by a different color or by a number marked on the insulation. In order to avoid electromagnetic interference caused by power cables laid nearby control cables may be shielded.

The electromagnetic shielding material, which is wrapped around the cable underneath the outer jacket serves to prevent electrical noise from affecting the transmitted signal, and to reduce electromagnetic radiation emission from the cable itself. Shielding is typically comprised of metal braiding, metal tape or foil braiding. A shielded cable assembly may also feature a special grounding wire known as a drain wire.

See the Guidelines for Control and CT Wiring found in this dropdowm menu.

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Control Cable Summary:

Control Wire Summary

Current Transformer Cable and Wiring Guidelines and Specification

For CTs, most of the field (cable) wiring sizes are done with 10 AWG. The resistance of #10 wire is easy to remember since it is approximately 1 Ohm per 1000 feet.

CT secondary circuit must be grounded, and grounded at one point only. Important to remember if the secondary of CT is left open (unloaded) a risk of explosion exists.

The electromagnetic shielding material, which is wrapped around the cable underneath the outer jacket serves to prevent electrical noise from affecting the transmitted signal, and to reduce electromagnetic radiation emission from the cable itself. Shielding is typically comprised of metal braiding, metal tape or foil braiding. A shielded cable assembly may also feature a special grounding wire known as a drain wire.

See the Guidelines for Control and CT Wiring found in this dropdowm menu.

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Current Cable Transformers Specifications

CT Cable Summary

EDM's intent of this Guideline is to establish uniform practice of installing, identifying and terminating control and communication cables in all of EDM's design projects. These guidelines are proven to reduce installation, commissioning and troubleshooting time in the field during and after construction.

This includes:

Guidelines for cable selection.

Guidelines for cable numbering.

Guidelines for wire colors.

Guidelines for wire numbering.

Guidelines for wiring terminations of cable into junction boxes, equipment cabinets, and marshalling racks.

Guidelines for CT Cables.

Guidelines for CT Wires.

This is applicable to all CT and Control Cables 600 volts or less.

EDM Control Cables Installation - General

Outdoor Cables

EDM uses Shielded control cables between outdoor equipment and the control building (Marshalling Rack) for all circuits in all project outdoor cables.

All control cables shall be identified by the EDM's cable numbering system, User input is incoporated as much as possible into the cable and wire labeling, but for consistancy EDM's standard labeling format (3 components) is used in the program as follows:

Prefix ID- clients identification.

Equipment ID - equipment identification.

Cable Number - cable identification (describes the function and unique number).

Example: EDM-HVT1-ALM1

EDM limits each component to 3 or 5 letters to reduce the length of the descriptor as much as possible.

Both ends of the cable shall be tagged in the field for easy identification.

User to determine if spare cables are required.

All control cables entering the control building will normally be terminated on marshalling racks and all cable shields to be grounded at the marshalling rack. CLA Electiral Standards provides details for grounding the shield at the Marshalling Racks.

When selecting the control cables for terminating circuits EDM calculates the proper cable that is to be used with the minimum number of spare wires. EDM sets the number of allowable spares per cable at 2 per cable with no exceptionand spare wires are always terminated to terminal blocks.

Indoor Cables

Indoor cable runs from the Marshalling Rack to the appropriate module rack as well as rack to rack wiring runs shall be made with 2C#14, 4C#14, 8C#14 or 10C#14 indoor cable.

Wires

Keep all wires of one control circuit in the same cable. Do not combine AC station service, DC station service, VT, CT wires in the same cable.

All control cables shall be identified by the EDM's cable numbering system, User input is incoporated as much as possible into the cable and wire labeling, but for consistancy EDM's standard labeling format (2 components) is used in the program as follows:

Equipment ID - equipment identification plus function.

Wire Number - wire identification (describes the function and unique number).

Example: T1ALM-101, T1ALM-102, T1ALM-103, 4, 5 etc.

Both ends of the wire shall be tagged in the field for easy identification.

All spare wires shall be terminated to terminal blocks at both ends of the cable, including wires of spare cables.

Wire Colors

ICEA (Insulated Cable Engineers Association) Standard S-73-532, this standard describes different methods of identification and provides tables of color sequences to use with these methods. Although there are many methods and color sequences, Methods 1, 3, and 4 are the most widely used.

Method 1 – Different color insulation with tracers.

Method 3 – Single color insulation with surface printing of number and color designations.

Method 4 – Single color insulation with surface printing of numbers only.

All wires shall be terminated according to the number or color sequence outlined in the E2 color table depending on the color Method chosen. For example, if Method 4 is chosen (cable numbers), all terminations must be in consecutive numerical order from 1 to 30, depending on the number of wires per cable chosen, in the Marshalling Racks.

As well, if Methods 1 or 3 are chosen, the wires are terminated as per the order of the colors listed in the E2 Color Table. (See EDM's Quick Calculator - Cable Insulation for E1 and E2 Color Tables).

CT Cables

All CT cables shall be identified by the EDM's cable numbering system, User input is incoporated as much as possible into the cable and wire labeling, but for consistancy EDM's standard labeling format (3 components) is used in the program as follows:

Prefix ID- clients identification.

Equipment ID - equipment identification.

Cable Number - cable identification (describes the function and unique number).

Example: EDM-HVT1-1C0

EDM's convention for CT Cables is as follows; the cable is associated with HVT1 Transformer, connected to the transformer's first primary CT identified by 1 in the cable number, the C identifies it as a CT function, and the 0 is the first circuit located between the C.T junction box and the Marshalling Rack panel. (First terminal is defined as the terminal located at C.T junction box and referred to as the “0" circuit, the next connected device in the circuit the cable number would be "1C1" and "1C2“ etc.

EDM limits each component to 3 or 4 letters to reduce the length of the descriptor as much as possible.

CT Wires

All CT wires shall be identified by the EDM's wire numbering system, User input is incoporated as much as possible into the cable and wire labeling, but for consistancy EDM's standard labeling format (2 components) is used in the program as follows:

Equipment ID - equipment identification.

Wire Number - wire identification (describes the function and unique number).

EDM's convention for CT wires is as follows: the wire is associated with HVT1 Transformer, connected to the transformer's first primary CT identified by 1 in the wire number, the C identifies it as a CT function, and the 0 is the first circuit located between the CT Junction Box and the Marshalling Rack panel and referred to as the “0" circuit. The number 1 defines A phase, 2 defines B phase, 3 defines C phase and N defines Neutral wire, the wire numbers would be "1C01", "1C02“, 1C03 and 1C0N.

The transformer's second primary CT would be identified by 2 in the wire number, therefore, the wire numbers would be "2C01", "2C02“, 2C03 and 2C0N. This convention would be carried through with all the tranformer CTs.

In the CT Circuits, the next device in line, the CT wire number would be 1c11, next device in line the CT wire number would be 1c21 etc. this is carried through for all the transformer CTs.

Both ends of the wire shall be tagged in the field for easy identification.