Traction Power Rectifier Transformers IEEE Std. 1631.1

IEEE Std 1653.1

IEEE Standard Practices and

Requirements for Traction Power Rectifier Transformers

1

Traction Power Rectifier Transformers IEEE Std. 1631.1

Version: 1/25/2005

VEHICULAR TECHNOLOGY SOCIETY

RAIL TRANSIT VEHICLE INTERFACE STANDARDS COMMITTEE

IEEE Traction Power Substation Standards Subcommittee (TPSSC)

Working Group 21

Abstract: This standard is a basis for the establishment of performance, interchangeability, and safety requirements of traction power rectifier transformersand provides assistance in the proper selection of such transformers. Electrical and mechanical design, manufacturing, and testing requirements are set forth for traction power rectifier transformers of all power ratings operating at DC electrification systems at voltages up to 1,500 VDC. The standard covers liquid-immersed and dry-type transformers, including those with encapsulated windings and cast coils.

Keywords: traction power rectifier transformers, electrical requirements, mechanical requirements, service conditions, rating, design, construction, short circuit, protection, indication, design optimization, testing.

Table of Contents

1

Traction Power Rectifier Transformers IEEE Std. 1631.1

1Overview

1.1Scope

1.2Purpose

1.3Mandatory and Recommended Requirements

2References

3Definitions

4Service Conditions

4.1General

4.2Usual Service Conditions

4.2.1Ambient Temperature

4.2.2Fluctuating Loads

4.2.3Short Circuits

4.2.4Voltage and Current Harmonics

4.2.5Operation Above Rated Voltage or Below Rated Frequency

4.2.6Vibrations

4.2.7Altitude

4.3Unusual Service Conditions

5Rating Data

5.1Continuous Rating

5.2Overload Ratings

5.3Load Cycle

5.3.1General

5.3.2Standard Load Cycles

5.3.3Custom Load Cycle

5.4Winding Temperature Limits

5.4.1Light Traction Service Load Cycle

5.4.2Heavy Traction Service Load Cycle

5.4.3Extra-Heavy Traction Service Load Cycle

5.4.4Custom or User-Defined Load Cycle

5.5Nameplates

6Design

6.1Taps

6.2Impedance

6.2.1Secondary Winding Coupling

6.2.2Standard and Reduced Regulation

6.3Two-Winding Transformers

6.3.1Winding Connections for Six-Pulse Rectification

6.3.2Winding Connections for Twelve-Pulse Rectification

6.4Three-Winding Transformers

6.4.1Winding Connections Six-Pulse Rectification

6.4.2Winding Connections for Twelve-Pulse Rectification

6.4.3Tertiary Winding for Auxiliary Power

6.5Four-Winding Transformers

6.5.1Winding Connections for Twelve-Pulse Rectification

6.5.2Quaternary Winding for Auxiliary Power

6.6Secondary Winding Voltage, Current, and Impedance Differences

6.6.1Voltage Difference

6.6.2Current Difference

6.6.3Impedance Difference

6.7Design Optimization

6.7.1General

6.7.2Life Cycle Cost

6.7.3Efficiency

6.7.4Loss Measurement Temperature

6.8Life Expectancy

7Construction

7.1Core and Winding Construction

7.2Connecting Cables

7.3Insulation System

7.4Winding Conductors

7.5Assembled Coils

7.6Thermocouple Location

8Short Circuit Characteristics

8.1Liquid-Filled Transformers

8.2Dry-Type Transformers

9Protection

9.1General

9.2Overcurrent Protection

9.2.1Overload and Phase-Fault Protection

9.2.2Ground-Fault Protection

9.3Overtemperature Protection

9.4Unbalance Protection

9.5Gas Pressure Protection

9.6Gas Pressure Relief Device

9.7Overvoltage Protection

9.8Accessories

10Testing

10.1General

10.2Factory Testing

10.2.1General

10.2.2Load Cycle Test

10.2.3Short Circuit Test

10.2.4No-Load Loss Test

10.2.5Load Losses Test at Various Loadings

10.2.6Partial Discharge Test

10.2.7Commutating Impedance

10.3Field Testing

10.3.1Pre-Energization Inspection Testing

10.3.2Line-to-Rail Short Circuit

10.3.3Line-to-Ground Short Circuit

11Tolerances

12Winding Connection for Shipment

13Bibliography

1

Traction Power Rectifier Transformers IEEE Std. 1631.1

IEEE Standard Practices and

Requirements for Semiconductor

Traction Power Rectifier Transformers

1Overview

1.1Scope

This standard covers design, manufacturing, and testing unique to application of power rectifier transformers intended to operate in DC rail transportation and trolley bus substation applications.

1.2Purpose

Provide a supplement to IEEE Std C57.18.10 to cover requirements specific to traction power rectifier transformers supplying power to DC powered rail and trolley bus transportation equipment. The purpose of this standard is to provide minimum uniform transportation industry requirements.

1.3Mandatory and Recommended Requirements

The words “shall” and “must” indicate mandatory requirements. The words “should” and”may” indicate requirements that are recommended and permitted, but not mandatory.

2References

References should be made to the latest versions of the following standards:

IEEE Std C57.12.00, Standard General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers (ANSI)

IEEE Std C57.12.01, Standard General Requirements for Dry Type Distribution and Power Transformers Including Those with Solid Cast and/or Resin-Encapsulated Windings

IEEE Std C57.12.80, Standard Terminology for Power and Distribution Transformers

IEEE Std C57.12.90, Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers and Guide for Short-Circuit Testing of Distribution and Power Transformers (ANSI)

IEEE Std C57.12.91, Test Code for Dry-Type Distribution and Power Transformers

IEEE Std C57.18.10, Standard Practices and Requirements for Semiconductor Power Rectifier Transformers

IEEE Std C57.96, IEEE Guide for Loading Dry-Type Distribution and Power Transformers

IEEE Std C.57.120, IEEE Loss Evaluation Guide for Power Transformers and Reactors

IEEE Std 100, IEEE Standard Dictionary of Electrical and Electronics Terms

3Definitions

Standard transformer terminology available in IEEE Std C57.12.80 shall apply. Other electrical terms are defined in the IEEE Std 100.

Dry-Type Transformer. Transformer cooled by the natural circulation of air. Dry-type transformers include transformers with encapsulated windings or cast coils.

Life Cycle Costor Total Ownership Cost: the sum of the procurement cost and the cost of energy losses over the transformer expected life.

Liquid-Immersed Transformer. Transformer having its core and coils immersed in liquid. Cooling is achieved by natural or forced circulation of air over cooling surfaces and by natural or forced circulation of liquid over the core and coils.

Load Factor: Ratio of average power demand to peak power demand in the same interval of time.

Multiple-Feed System: Traction electrification system in which substation feed sections of the distribution system at multiple points. Under normal conditions, the distribution system operates as a continuous bus where all sectioning gaps are bypassed by closed circuit breakers or disconnect switches.

Power Demand Analysis and Load-Flow Study: A computer-aided study using specially written computer program to calculate the combined performance of the traction power supply and traction power distribution systems with operating trains. The study results normally include distribution system voltages, distribution system currents, substation power demand requirements and substation energy consumption.

Rolling Stock: Transit vehicle or train receiving motive power from a traction power distribution system.

Traction Electrification System: Traction power supply, traction power distribution, and traction power return systems.

Traction Power Distribution System: Overhead catenary system, overhead contact wire system, third rail system, four-rail system, or guideway contact busbar system which may be accompanied by parallel along track feeders. The system also includes positive feeders from substation circuit breakers to the trackside.

Traction Power Supply System: Traction power substations located at predetermined spacings along the system route.

Traction Power Return System: Running rails or guideway contact busbar system, impedance bonds, and cross-bonds. The system also includes negative feeders from the trackside to substation negative busbar.

4Service Conditions

4.1General

Transformers conforming to this standard shall be suitable for operation at rated kVA under following usual service conditions.

4.2Usual Service Conditions

4.2.1Ambient Temperature

Outdoor- and indoor-installed transformers shall be capable of operating in an average daily ambient temperature of 30°C, with a maximum ambient temperature of 40°C and minimum temperature of -20°C.

4.2.2Fluctuating Loads

Traction power rectifier transformers shall be capable of operating under rapidly changing and fluctuating loads typical of traction power systems. The load fluctuation is caused as rolling stock accelerates, decelerates, encounters alignment gradients, and enters different substation feeding sections.

4.2.3Short Circuits

Traction power systems are characterized by high incidence of short circuits. On occasions, a system may experience several short circuits in a day.

4.2.4Voltage and Current Harmonics

Traction power rectifier transformers shall be capable of operating under expected load with voltage and current harmonics caused by substation rectifiers and rolling stock propulsion system electronics. During preparation of transformer specification, the designer should contact the rectifier and rolling stock manufacturers, if known, and obtain the expected harmonic spectra under various loading conditions. As a minimum, the transformer manufacturer must receive the expected harmonic content at 100% loading and 450% loading.

In the event that the rectifier and rolling stock manufacturers are not known, the rectifier harmonic spectrum in accordance with IEEE Std C57.18.10 shall be used with a reasonable adjustment for rolling stock harmonics.

4.2.5Operation Above Rated Voltage or Below Rated Frequency

Traction power rectifier transformers shall be capable op operation above rated voltage or below rated frequency in accordance with IEEE Std C57.12.00.

4.2.6Vibrations

Traction power substations are generally located close to the system operating envelope. Therefore, the transformers will be subjected to the vibrations due to passage of trains.

4.2.7Altitude

The usual service altitude shall not exceed 3,300 ft (1,000 m).

4.3Unusual Service Conditions

Conditions other than those described in 4.2 are considered unusual service conditions. When prevalent, the conditions should be brought to the attention of those responsible for design and application of the transformer. Unusual service conditions may constitute any one or combination of the following:

  • Operation at higher than maximum ambient temperature
  • Lower than minimum ambient temperature
  • Operation above the load cycle
  • Operation in high altitude
  • Abnormal vibration or tilting

Further examples of unusual operating conditions are given in IEEE Std C57.12.00.

5RatingData

5.1Continuous Rating

The traction power rectifier transformer kVA rating shall be on the fundamental basis in accordance with IEEE C57.18.10. All electrical characteristics, such as efficiency, regulation, losses, impedance, and commutating impedance, shall use the fundamental kVA as the base kVA.

The thermal capability of the transformersshall be tested using root-mean-square (rms) kVAin accordance with IEEE C57.18.10. The rms kVA must include the fundamental kVA plus kVA due to the specified harmonics caused by rectifiers and rolling stock.

The transformer continuous rating should take into accountplanned load growth, compensate for a transformer or substation outage, and accommodate special or unusual transit system operation.

The continuous kVA rating is recommended to be the transformer self-cooled rating designated as follows:

  • Liquid-Immersed Transformers - Self-Cooled (ONAN)Rating
  • Dry-Type Transformers - Self-Cooled (AA)Rating

5.2Overload Ratings

In order to provide capability to service planned loadgrowth beyond the current projections,it necessary to specify overload ratings. The overload rating is recommended to be the transformer air-cooled rating designated as follows:

  • Liquid-Immersed Transformers - Self-Cooled/Forced Air-Cooled (ONAN/ONAF) Rating
  • Dry-Type Transformers - Self-Cooled/Forced Air-Cooled (AA/AF) Rating

It is recommended that the transformers are rated so that they can be initially installed as self-cooled. The fans, if needed, are recommended to be installed in the future when the load increases beyond the projected load growth. This requires that the transformers are specified and manufactured with full provisions for future fan installation.

In unusual situations where space for liquid-immersed transformers is limited, air- and oil-cooled rating may be used, designated as follows:

  • Self-Cooled/Forced Air-Cooled/Forced Liquid-Cooled (ONAN/ONAF/OFAF) Rating

The designer should be aware that provision of cooling fans and oil pumps introduces additional complexity, maintenance, and possibly remote supervision.

5.3Load Cycle

5.3.1General

Because of the traction load fluctuation and high demand peaks, the traction power rectifier transformers must have the capability to supply the rated power continuously with a superimposed overload cycle representing a rush period operation twice a day.

5.3.2Standard Load Cycles

Normally, the overload cycle is specified in accordance with theIEEE Std C57.18.10. The following standard load cycles are recommended for traction service:

5.3.2.1Light Traction Service Load Cycle

The Light Traction Service capability is defined as follows:

  • 100% of rated power continuously
  • 150%of rated power for 2 hours
  • 200% of rated power for 1minute

Subject to traction power system load-flow study of the transit system, the Light-Traction Service load cycle can be used for street car, trolley bus, and some people mover transit applications.

5.3.2.2Heavy Traction Service Load Cycle

The Heavy Traction Service capability is defined as follows:

  • 100% of rated power continuously
  • 150%of rated power for 2 hours
  • 300% of rated power for 1minute

Subject to traction power system load-flow studyof the transit system, the Heavy-Traction Service load cycle can be usedfor street car, trolley bus, people mover, and some light rail transit applications.

5.3.2.3Extra-Heavy Traction Service Load Cycle

The Extra-Heavy Traction Service capability is defined as follows:

  • 100% of rated power continuously
  • 150%of rated power for 2 hours
  • 300% of rated power for five equally spaced periods of 1 minute
  • 450% of rated power for the final 15 seconds

Subject to traction power system load-flow study of the transit system, the Heavy-Traction Service load cycle can be used for all light rail transit applications and all heavy rail applications.

5.3.3Custom Load Cycle

In transit applications where the overload cycle is substantially different than the Light-Traction Service,Heavy-Traction Service, or the Extra-Heavy Traction Service as defined by C57.18.10, a custom load cycle may be specified.

The custom load cycle should be developed based on the traction power system load-flow studies, load measurement on existing systems, or equivalent calculation or simulation methods. Unusual overload operation associated with such conditions as special events and adjacent unit failure shall be assessed based on actual operating history of similar systems. This assessment is to be used to define the amount of unusual overload and the portion of total operating time this overload represents.

The results of these analyses shall be appliedin accordance with IEEE 57.96 to determine the thermal capacity necessary to meet the required design life. This required design life shall be specified.

Operation, especially during unusual overload conditions, may result in insulation hot spot temperatures exceeding those of the insulation class, which is defined by 20 year life at class temperature. Design tests must be performed to demonstrate that these peak temperatures will not result in mechanical or dielectric discontinuities, which could result in catastrophic failure. Suggested design tests should include thermal shock and dielectric tests at peak temperature on the first unit which would represent stresses in the production units.

5.4Winding Temperature Limits

5.4.1Light Traction Service Load Cycle

Winding hottest-spot temperature and average winding temperature shall not exceed the limits given in Table 1 for liquid-immersed transformers and the limits given in Table 2 for dry-type transformers, taking into account the maximum ambient temperature specified. The limits apply at the tap connection resulting in the highest losses.

The hottest-spot temperature shall be determined by calculation or from temperature test data. The average temperature shall be measured by the resistance method in accordance with IEEE Std C57.12.90 and IEEE Std C57.12.91.

Table 1 – Limits of Temperatures for Liquid-Immersed Rectifier Transformer Windings

Light Traction Service

Insulation System Temperature Class (°C) / Load in % of Rated Power / Winding Hottest-Spot Temperature (°C) / Average Winding Temperature (°C) / Operation
120 / 100 / 110 / 105 / Continuous at rated power until temperature steady-state.
200 / 140 / 135 / Transformer reached a steady-state temperature at 100% load and operated at150% overload for two hours, at 200% overload for one minute.

Table 2 – Limits of Temperatures for Dry-TypeRectifier Transformer Windings

Light Traction Service

Insulation System Temperature Class (°C) / Load in % of Rated Power / Winding Hottest-Spot Temperature (°C) / Average Winding Temperature (°C) / Operation
150 / 100 / 140 / 90 / Continuous at rated power until temperature reaches steady-state value.
200 / 150 / 100 / Transformer reached a steady-state temperature at 100% load and operated at150% overload for two hours, at 200% overload for one minute.
185 / 100 / 175 / 120 / Continuous at rated power until temperature reaches steady-state value.
200 / 185 / 130 / Transformer reached a steady-state temperature at 100% load and operated at150% overload for two hours, at 200% overload for one minute.
220 / 100 / 210 / 150 / Continuous at rated power until temperature reaches steady-state value.
200 / 220 / 160 / Transformer reached a steady-state temperature at 100% load and operated at150% overload for two hours, at 200% overload for one minute.

5.4.2Heavy Traction Service Load Cycle

Winding hottest-spot temperature and average winding temperature shall not exceed the limits given in Table 3 for liquid-immersed transformers and the limits given in Table 4 for dry-type transformers, taking into account the maximum ambient temperature specified. The limits apply at the tap connection resulting in the highest losses.

The hottest-spot temperature shall be determined by calculation or from temperature test data. The average temperature shall be measured by the resistance method in accordance with IEEE Std C57.12.90 and IEEE Std C57.12.91.

Table 3 –Limits of Temperatures for Liquid-Immersed Rectifier Transformer Windings

Heavy Traction Service

Insulation System Temperature Class (°C) / Load in % of Rated Power / Winding Hottest-Spot Temperature (°C) / Average Winding Temperature (°C) / Operation
120 / 100 / 110 / 105 / Continuous at rated power until temperature steady-state.
300 / 140 / 135 / Transformer reached a steady-state temperature at 100% load and operated at150% overload for two hours, at 300% overload for one minute.

Table 4 – Limits of Temperatures for Dry-TypeRectifier Transformer Windings

Heavy Traction Service

Insulation System Temperature Class (°C) / Load in % of Rated Power / Winding Hottest-Spot Temperature (°C) / Average Winding Temperature (°C) / Operation
150 / 100 / 140 / 90 / Continuous at rated power until temperature reaches steady-state value.
300 / 150 / 100 / Transformer reached a steady-state temperature at 100% load and operated at150% overload for two hours, at 300% overload for one minute.
185 / 100 / 175 / 120 / Continuous at rated power until temperature reaches steady-state value.
300 / 185 / 130 / Transformer reached a steady-state temperature at 100% load and operated at150% overload for two hours, at 300% overload for one minute.
220 / 100 / 210 / 150 / Continuous at rated power until temperature reaches steady-state value.
300 / 220 / 160 / Transformer reached a steady-state temperature at 100% load and operated at150% overload for two hours, at 300% overload for one minute.

5.4.3Extra-Heavy Traction Service Load Cycle

Winding hottest-spot temperature and average winding temperature shall not exceed the limits given in Table 5 for liquid-immersed transformers and the limits given in Table 6 for dry-type transformers, taking into account the maximum ambient temperature specified. The limits apply at the tap connection resulting in the highest losses.