Protection for a Power Transformer

Transformer Protection

Power Transformer is an essential electrical component. An engineer like me, who only depends on the transformer then it’s really important to keep the transformer active for 24/7. If there is any problem with the transformer then all the machinery inside of the factory floor will be silent and zero production will come.

When you are having a problem with your transformer then it may take a long time to repair it. So it’s better to protect the power transformer in the first place. In this post, I will discuss all the power transformer protection procedures that you can apply in your daily work. So let’s go.

Protection for a Power Transformer:

Abnormal Condition	Protection	Remarks
Incipient faults for below oil level resulting in decomposition of transformer oil.	The Buchholz relay sound alarm. (The GAS activated relay) Sudden Pressure Relay. The pressure relief valve.	Normally Buchholz relay used for a power transformer when its rating is 500 KVA or above.
A large number of internal faults like phase to phase, phase to ground, below the oil level. Fault while tap changing.	The Buchholz relay trips the circuit breaker.	The Buchholz relay is too slow and less sensitive. Buchholz relay for the tap changing also.
	Percentage of differential protection. The high-speed high set overcurrent relay	Percentage of differential protection used for a transformer when its above 5 MVA.
Saturation of transformer magnetic circuit.	The over fluxing protection. The overvoltage protection.	It’s important for the generator transformer and the feeder transformer.
Earth Fault	Differential Protection	For the transformer and above 5 MVA.
Earth Fault	Earth Fault Relay	Instantaneous resistive earth fault relay. The time lag earth fault relay.
Trough Fault	Graded time lag overcurrent relay. HRC fuses.	It’s the protection of the distribution transformer. For a small distribution transformer up to 500 KVA.
Transformer Overloads	The thermal overload relay. Temperature relays sound alarmed.	Normally temperature indicators are provided with the transformer. Temperature increases are also indicated on the control board then fans start at a certain temperature.
High Voltage surges due to switching, lightning.	Horn gap. The lightning arrestor.	It’s not favored for important transformers. In addition to lightning arrestors for the main incoming line.
Small Distribution Transformer. A transformer in important locations and ratings is above 500 KVA.	Only for high voltage fuses for earth faults protection and the phase fault protection. Overload protection normally not provided. For an important transformer of about 500 KVA. Overload relay and instantaneous earth fault relays. The restricted earth fault relays. The overcurrent protection, Buchholz relay.
The transformer is about 5 MVA and above	Differential Protection. The restricted earth fault protection. Over fluxing protection. Sudden pressure relays. Overcurrent protection. Buchholz relay
The under-voltage and overvoltage relay: when necessary.