SERGI - Research Program

Results [6]

A. Arc energy and transformer power are not key parameters for transformer tank explosion
prevention

1. Saturation of gas production due to plasma and gas thermal screens

The huge gas volume created during the first milliseconds is surrounding the electrical arc and the energy is then used to create plasma. As a result, plasma and gas thermal screens do not allow the arc energy to generate gas after creation of the first pressure peak
Plasma is a gas heated at very high temperature locally ionized
For a 100 Mega Joule electrical arc inside the oil, the first Mega Joule creates 2.3m3 (80 ft3), of explosive gas. The other 99 Mega Joule add only 2 m3 (70 ft3). As a result, any electrical arc is very dangerous

EXPLOSIONS HAVE A WEAK RELATION WITH ARC ENERGY

Tests have demonstrated that gas production by an electrical arc is quickly saturated by creation of plasma, 2.3 m3 (80 ft3) for the first Mega Joule against only 4.3 m3 (150 ft3) for 100 Mega Joules.

2. Relation between electrical arc energy and maximum dynamic pressure peak

One Mega Joule creates 2.3m3 (80 ft3) of explosive gas
100 Mega Joules create only a total of 4.3m3 (150 ft3) of explosive gas
The tests have not shown a clear relation between electrical arc energy and maximum dynamic pressure peak

100 Kilo Joules can generate a peak of 10 bar (145 psi)
1000 Kilo Joule can generate a peak of 3 bar (43 psi)

3. Conclusion: Transformer explosions have a weak connection with arc energy and transformer power.

B. TRANSFORMER PROTECTOR Efficiency

The TP operational parameters are independent from the arc position inside the tank. Even for the arcs located in position C (Figure 1), the pressure wave propagated and always activated the TP before the tank could explode.
The pressure gradients and tank depressurisation encountered in the tests were in agreement with the values calculated before with the MTH model.
The TP efficiency was demonstrated. As shown in figures 2 and 3, the TP absorbs a pressure gradient of 3,900 bar/sec (56,500 psi/sec) and the tank pressure returns to the Rupture Disk set point only 3 milliseconds after operation.
Analysis showed that the MTH Model results and especially the Pressure Wave propagation matched very closely the tests measurements.

Test Configuration

Pressure variation during TRANSFORMER PROTECTOR activation

Pressure variations during TRANSFORMER PROTECTOR activation

C. Transformer Tank Resistance

     The TP has been tested with air-polluted oil delay the shock wave speed by a factor of 10, for the tank to see the
     pressure wave and static pressure rise 10 times longer.

     As a result, for the worst test the transformer tank has seen the pressure during 57 milliseconds before the TP
     operates. For non-polluted oil, 57 milliseconds corresponds to a dynamic pressure peak travelling distance of 68 meters
     (223 feet), far longer than the distance on the biggest existing transformers

D. Safety

     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.

E. Buchholz Not Activated

During all the tests, the Buchholz pressure and gas signals were activated. The speed of the phenomena is too fast for this
device

INADEQUATE ELECTRICAL PROTECTIONS

At the time of the creation of the electrical arc, 2.3m/3 (80 ft/3) of explosive gas are generated by the first Mega Joule in the first milliseconds, much too late and much too fast to avoid explosion with electrical protections.

	The MTH Model
	Comparison with the PRV
	Power Plant Transformers
	Pressure Wave Propagation Modelling
	MTH model and Transformer reliability
	Transformer Protector Tests
	Results