IEC 60076-24:2020 pdf download – Power transformers – Part 24: Specification of voltage regulating distribution transformers (VRDT.
5.3 Voltage steps Unless otherwise specified, voltage steps are 1,0 % up to 3,0 % and shall be agreed between manufacturer and purchaser. 5.4 Regulation range Unless otherwise specified, the on-load regulation range is ±5 % up to ±10 % of the rated voltage ratio for symmetrical regulation. 6 Service life Loading guides (IEC 60076-7 and IEC 60076-12) are applicable. Deviations shall be agreed between manufacturer and purchaser. The manufacturer shall indicate the number of operations for which the VRDT is designed. The manufacturer shall indicate a future need for firmware updates of the control unit. 7 Parallel operation of the VRDT For parallel operation of the VRDT, special precautions should be taken to avoid high circulating currents. NOTE Depending on the impedance of the connections between the VRDTs, significant circulating currents are possible (IEC 60076-8). A typical solution can be a master/follower arrangement or a single grid controller. 8 Loss level Measurement of the loss level shall be in accordance with IEC 60076-1. The maximum loss level for the VRDT (transformer and regulating unit) shall be compliant with local standards, for example, EN 50708. No-load and load losses shall include regulating unit losses. 9 Sound power level Measurement of the sound power shall be in accordance with IEC 60076-10. The maximum sound power level shall be compliant with local standards, for example, EN 50708. Operating noise during the switching process of voltage regulation should not be taken into account. This noise and its values shall be agreed between manufacturer and purchaser. 10 Rating plate Rating plate requirements are in accordance with IEC 60076-1, IEC 60076-11, and with applicable local standards, for example, EN 50708.
11 Tests 11.1 Routine tests Apply IEC 60076-1 and IEC 60076-11, but with different test sequences, in accordance with this document. 11.2 Functional tests With the regulating unit fully assembled on the transformer, the following sequence of operations shall be performed as a routine test, without any failure: a) with the transformer de-energized, three complete cycles of operation (a cycle of operation goes from one end of the tapping range to the other, and back again); b) with the transformer de-energized, and with the auxiliary voltage reduced to 85 % of its rated value, one complete cycle of operation; c) with the transformer energized at rated voltage and frequency at no load, one complete cycle of operation. 11.3 Type tests If the regulating unit contains electronic components, the test conditions shall be agreed between manufacturer and purchaser. If the operation of the regulating unit occurs in conditions that differ from those of IEC 60076-1, a heat run test according to IEC 60076-2 shall be agreed between purchaser and manufacturer. With the regulating unit fully assembled on the transformer, the following sequence of operations shall be performed, without any failure: With one winding short-circuited and, as far as practicable, rated current in the tapped winding, 10 cycles of tap-change operations across the complete range. NOTE In order to check the correct coordination of over-current protection and to have all information regarding the operation of the VRDT, the purchaser can request the measurement of the impedance voltage and load losses on all the taps, related to the high voltage (HV) rated voltage and rated power of the VRDT. The functional tests shall be repeated.
11.5 Tests for the control unit (electronic or data transfer part) 11.5.1 Functionality test during erection and commissioning The transformer is connected on either the HV or LV side and the other side is open for testing. Voltage shall be measured at the open side. The control unit is in manual operation mode and is then switched through the complete regulation range. For each switching operation, the relative change in the measured voltage shall be equivalent to the regulation steps. If the VRDT has an automatic mode then with rated voltage applied to the HV, manually set the regulator to one of the extreme positions, then switch to automatic mode and check that the system regulates the LV voltage to the rated value.