SERGI - Transformer Protector Test

Transformer Protector Tests

2 series of tests of the TRANSFORMER PROTECTOR have been performed in 2002 and 2004. The worst conditions to provoke a transformer explosion were created. An electrical arc between electrodes located inside the oil was ignited for the 62 tests. The aim was to:




Picture of the CEPEL test area with 3 transformers equipped with TRANSFORMER PROTECTOR including 1 OGST

•prove the TRANSFORMER PROTECTOR efficiency for pressure gradients up to 4 000 bar/second (58 000 psi/s);
•compare the MTH preliminary calculations with real cases of transformer faults;
•increase SERGI knowledge on the electrical arc inside oil;
•calculate the pressure wave propagation;
•measure the operation of traditional transformer protections;
•measure and define a law for gas generation volume during short-circuit.

Tests at Electricité de France (EDF), 2002 [6]

The EDF High Voltage Laboratory has performed 28 tests on a 160 kVA transformer.
Electrical arcs were ignited with current faults from 2.5 to 7.5 kilo Amperes, arc energies went up to 300 kilo Joules and pressure gradients varied from 200 to 1 200 bar/second (2 900 to 17 400 psi/s).
During those tests, the rapid gas expansion generated by the oil decomposition before the arc was filmed (cf. side picture). Also, several gauges located around the tank measured the pressure waves that followed the gas creation.


	Gas generated during rupture of insulation before the electrical arc inside the tank



		2 ms

3 ms


	4 ms


	Time, milliseconds




		5 ms

Tests at CEPEL Laboratory, Brazil, 2004 [6]

The CEPEL High Voltage Laboratory has performed 34 tests on 3 transformers of 6, 10 and 20 MVA with current faults up to 15 kilo Amperes and energies up to 2,4 Mega Joules. Half of the tests were realized under vacuum conditions to measure the total volume of gas produced during the arc generation.
Different ignition locations for the arc were chosen to study the TRANSFORMER PROTECTOR behaviour (see besides picture).


•A, in front of the Depressurisation Set; •B, at the opposite side; •C, diametrically opposed to the TRANSFORMER PROTECTOR Decompression Chamber. Measurements taken enabled to study the pressure wave propagation.

Results

•The pressure gradients and tank depressurisation encountered in the tests were in agreement with the values calculated beforehand using the MTH model [1 to 4]. •The efficiency of the TRANSFORMER PROTECTOR was demonstrated. As shown besides, the TRANSFORMER PROTECTOR absorbs a pressure gradient of 3 900 bar/second (56 500 psi/s) and the tank pressure returns to the Rupture Disk set point only 3 milliseconds after operation. •The besides graph illustrates that the stronger the short-circuit is, the faster the TRANSFORMER PROTECTOR reduces the pressure inside the tank. This exceptional efficiency of the TRANSFORMER PROTECTOR was already emphasized in 2001, publication [3]. •The TRANSFORMER PROTECTOR operational parameters are independent from the arc position inside the tank. Even for the arcs located in position C, the pressure wave propagated and always activated the TRANSFORMER PROTECTOR before the tank could explode. •Analyses showed that the MTH Model results and especially the Pressure Wave Propagation were very accurate with tests measurements. •All flammable gases created by the electrical arc were always exhausted from the Oil-Gas Separation Tank at the ambient temperature to atmosphere, and were never set on fire. Therefore, it was demonstrated that gas self ignition to the atmosphere is impossible. •During all the tests, the Buchholz pressure and gas signals were never activated as the speed of the phenomena is too fast for these devices.




	The 3 different arc ignition locations



	Pressure variation during TRANSFORMER PROTECTOR activation



	Activation time versus Energy

Test Certificate

•The TRANSFORMER PROTECTOR activated successfully during the 62 tests, depressurized the transformer and prevented the tank explosion and permanent deformation. CEPEL provided a Test Attestation for the 34 tests carried out at their High Voltage Laboratory [15].