Special Transformers

 

Grounding Transformer


Grounding Transformers are intended to establish an artificial neutral point for ungrounded three phase power systems. The kVA rating of an earthing transformer is contingent upon the normal line-to-neutral voltage and the magnitude of fault current for a specified duration, typically ranging from seconds to minutes. In the event of line-to-ground faults, these transformers offer a direct path for fault currents to ground, thereby constraining fault currents and transient over-voltages. Grounding Transformers typically handle short-circuit ground current until the circuit breaker resolves the fault. Consequently, they are equipped with short- time ratings. We have hermetic type, dry type and oil type transformers.

 
Motor Starting Auto-Transformers

 

Motor Starting Auto-Transformers (MSA) serve to mitigate inrush current by decreasing the applied voltage during the start-up phase of both induction and synchronous motors. Direct-online starting of a motor usually generates voltage flicker and mechanical stress to the equipment. To circumvent these issues, starting the motor at a reduced voltage is necessary a task accomplished through the use of an auto-transformer.

 

Auto-transformer significantly reduce the high starting current while providing moderate starting torque. They typically feature voltage taps set at 50%, 65% and 80% of the rated voltage.

 

Unlike reactor-based motor starters where motor voltage remains fixed, auto- transformers allow for further reduction in starting current while maintaining the same starting torque. During the startup phase the motor is connected to the taps of the auto-transformers, resulting in lower starting voltage and consequently lower current draw, yielding less torque compared to connection to the line voltage.

 

 

Grounding Transformers [ZN (Zigzag), ZNyn, YNd(open), Ii0]

 

Grounding Transformers are designed to provide an artificial, neutral point for ungrounded three phase power systems.

 

During the line-to-ground faults, grounding transformers provide an easy path to ground faults, thus limit the fault currents and transient over-voltages.

 

Grounding transformers normally carry short-circuit ground current until the circuit breaker clears the fault. Therefore, they have short time ratings.

 

The kVA rating of a earthing transformer depends on the normal line-to-neutral voltage and the fault current value for a specified time, such as seconds to minutes.

 

Technical Specifications

  • Types: Dry or oil-immersed [ZN (Zigzag), ZNyn, YNd(open), Ii0]
  • Voltage: Up to 36 kV
  • Current: Up to 3000 A*
  • Duty (seconds): 10 /30 / 60 or others
  • Cooling method: ONAN,ONAF, AN, AF
  • Frequency: 50 Hz / 60 Hz
  • Installation: Indoor / Outdoor
  • Ambient Temperature: -30°C to 55°C*
  • Standards: IEC 60076-6, IEC 60076-1
  • Enclosure Options: Transformer cabinets for any IP degrees with CT, VT, Isolation switch

*Consult factory for higher values.

 

Test List

  • Visual & Dimensional Check
  • Measurement of Voltage Ratio
  • Measurement of Winding Resistance
  • Measurement of Zero Sequence Impedance
  • Measurement of No-Load Loss and Current
  • Measurement of Short-Circuit Impedance and Load Loss
  • Dielectric Tests
  • Separate Source AC Withstand Voltage Test
  • Induced AC Withstand Voltage Test
  • Lightning Impulse Test
  • Temperature Rise Test
  • Final Check

For special tests, please contact us.

 

 

Motor Starting Auto-Transformers

 

Motor Starting Auto-Transformers reduce the inrush current by stepping down the applied voltage during the start-up operation of induction and synchronous motors.

Direct-online starting of a motor usually generates voltage flicker and mechanical stress to the equipment. To avoid this, the motor must be started at reduced voltage, which can be achieved by using an auto-transformer. The auto-transformer greatly reduces the high starting current with moderate starting torque.

 

Auto-transformers are typically designed with voltage taps of 50%, 65% and 80% of the rated voltage. In contrast to reactor based motor starters, the motor voltage is fixed. Thus, additional reduction in starting current is achieved using the same starting torque.

The motor is connected to the taps of the auto-transformer during the reduced voltage starting period. With lower starting voltage, less current is drawn by the motor, which therefore develops less torque then if it were connected to the line voltage.

 

Starting Characteristics

Motor terminal voltage is less than line voltage (by transformer ratio)

Motor current exceeds line current (by inverse of transformer ratio)

Starting torque is reduced by the square of the motor terminal voltage

 

Technical Specifications

  • Autotransformer types: Dry type cast resin or oil-immersed
  • Rated voltage: Up to 15kV
  • Rated Current: Up to 1600A*
  • Frequency: 50 Hz / 60 Hz
  • Insulation Class: Up to 155°C
  • Winding: Copper or aluminium
  • Standards: IEC 61558, IEC 60076-2
  • Installation: Open frame construction for low voltage auto-transformers
  • Ambient Temperature: -30°C to 55°C
  • Options: Complete solution as motor starter panel with autotransformer, Thermostats

*Consult factory for higher values.

 

 

High Current Transformer

 

High Current Transformers are designed to elevate and check the temperature of conductors at high current levels, in order to simulate the current loading conditions found in electrical circuits.

 

High Current Transformers are designed as an open type transformer. They use the test object as their secondary coil, or have 1- or 2-turn self secondary winding. The core temperature of the conductors depends on the short-circuit high current caused by the test object. Depending on the current going through the test object, the test temperature of the conductor will change. The loop temperature is measured by a thermocouple probe which is directly connected to conductor.

 

Technical Specifications

  • Transformer types: Dry type / Single phase / AC
  • Rated input voltage: 230 V / 400 V *
  • Rated output current: Up to 10 kA
  • Rated output voltage: 1 V, 2 V, 3 V, 4 V, 6 V, 10 V, 20 V, 40 V *
  • Rated capacity: Up to 120 kVA * for single phase
  • Frequency: 50 Hz / 60 Hz
  • Options: Complete solution with self-regulation of output voltage function for single phase or 3 phase

*Consult factory for higher values.

 

Typical Applications

  • Contact temperature measurement of MV switchgears
  • Temperature rise test for cables
  • CT injection testing
  • Short-circuit labs
  • Pipe pre-heating
  • CB testing
  • Electric ovens
  • Melting of aluminium