The electrical circuits in a substation need protection to limit the damages because of abnormal currents and over voltages. All equipment put in a ‘power transformers manufacturers India’ have standardized ratings for short-time face up to current and short period power frequency voltage.
Protection of transformers
The role of the protections is to confirm that these withstand limits never exceeded, so clearing the faults as quickly as possible. In addition to the current initial demand, a system of protection should be selective. Selective implies clearing any fault by the device of current interruption (circuit breaker or fuses) being the closest to the fault, even though the fault detection is by alternative protection source.
The electrical fuse in the first aspect should stay closed. For a transformer protected with MV fuses, the fuses should not blow.
They are generally two main devices that interrupt fault currents, circuit breakers, and fuses:
The circuit breakers relate to a protection relay having main functions:
- Measurement of the currents
- Detection of the faults
- Emission of a tripping order to the breaker
- The fuses blow below bound fault conditions.
Stresses generated by the availability
Two forms of over voltages might stress and even destroy a transformer:
- The lightning over voltages stroke falls on or close to an overhead line, provisioning the installation at the transformer.
- \For example, the switch over voltages, generated by the gap of an electrical fuse or a load brake switch.
Depending on the application, protection against these forms of voltage surges is also necessary and ensured by ZnO surge arresters ideally connected on the MV bushing of the transformer.
Stresses sue to load
A transformer overload is usually because of a rise in the installation’s apparent power demand (kVA) which is the consequence of either a progressive junction of masses or an installed extension.
The result of overload is the rise of oil temperature and windings of the transformer deduction in life.
The simulation predicates on the life and thermal time constant of the ‘power transformer manufacturers India.’ Some relays consider the result of harmonics because of non-linear masses like rectifiers, computers, variable speed drives, etc., and can also value the remaining time before the emission of the tripping order and the time delay before re-energizing the transformer.
- In addition, oil-filled transformers use thermostats to control the temperature of the oil.
- Dry-type transformers use heat sensors embedded within the hottest part of the insulation of the winding.
Each of those devices (thermal relay, thermostat, heat sensors) typically provides two levels of detection:
- A low level to generate an alarm to advise the upkeep workers,
- A high level to de-energize the transformer.
Internal faults in oil stuffed transformers
In oil stuffed transformers, internal faults classify as follow:
- Faults generating the production of gases, mainly:
- Micro arcs ensuing from early faults within the winding insulation
- Slow degradation of insulation materials
- Inter turns contact
- Faults generating internal overpressures with at the same time high level of line over currents:
- Phase to earth contact
- Phase to section contact.
These faults are also the consequence of external lightning or switching overvoltage.
As per ‘power transformer manufacturers India, ‘depending on the type of transformer, there are two types to sight internal faults touching an oil stuffed transformers:
- The Buchholz transformers
The Buchholz connects the tank of the transformer to the conservator. It traps the slow emissions of gasses and sights the flow back of oil because of the internal overpressures.
- The DGPT (Detection of Gas, Pressure, and Temperature)
This sort of transformer is factory-made up to around10 MVA. It also monitors the temperature of the oil.
Concerning the observance of gas and temperature, the Buchholz and also the DGPT offer two levels of detection:
- A low level to generate an alarm to advise the upkeep workers,
In addition, the Buchholz and also the DGPT are appropriate for oil leakage detection.
Overloads and internal faults in dry sort transformers
The dry transformers protect against overheating because of attainable downstream overloads by a zealous relay observance of thermal sensors embedded within the windings of the transformer.
The internal faults, principally bury turns and part to earth short circuits occurring within a dry transformer clear either by the electrical fuse or the fuses on the first aspect of the transformer.
Inner faults that need attention are:
- They generally generate moderate lines overcurrents. For example, when 5% of an HV winding short-circuited, the road current of the transformer doesn’t exceed a pair of In, for a short circuit touching 10% the winding the road current proscribed around three In.
- Fuses aren’t acceptable to clear properly such currents.
- Dry sort transformers aren’t with different protection devices like DGPT dedicated to internal faults detection.
Hence, internal faults generate a low line-level overcurrent that might not make safely clear by fuses but by using an excess relay of adequate characteristics.
Selectivity between the protecting devices upstream and downstream of the transformers
It is typical to ensure the property between the MV electrical fuse or fuse on a transformer’s primary circuit and the LV fuse.
The characteristics of the protection ordering the tripping or the MV electrical fuse or the in operation curves of the fuses should be like just in case of downstream fault the LV electrical fuse solely journeys. The MV electrical fuse should stay closed, or the fuse should not blow.
Conclusion
The protection of various circuits of power transformers manufacturers India is an essential aspect of the electrical department. Improper measures and carelessness can lead to fatal and hazardous outcomes. Therefore, various steps in the articles are to make the reader understand the list of measures one should take while dealing with a transformer, thus increasing its durability.
