Differential Transformer Protection

October 21, 2024 Post a Comment

Differential transformer protection

The protection of a transformer against the overloads is performed by a dedicated protection usually called thermal overload relay. This type of protection simulates the temperature of the transformer's windings. The simulation is based on the measure of the current and on the thermal time constant of the transformer.

What is the principle of differential protection?

Principle of differential protection Differential protection is based on the fact that any fault within an electrical equipment would cause the current entering it, to be different, from the current leaving it.

Which equipment is used for differential protection transformer?

Generally, differential relays are used to protect the equipment against internal faults. Merz price protection scheme is one form of the differential relay which is used to protect the stator winding of Alternator from the internal faults. Differential relay is also used for the protection of transformer winding.

What are the advantages of differential protection of transformer?

Differential protection schemes are mainly used for protection against phase-to-phase fault and phase to earth faults. The differential protection used for power transformers is based on Merz-Prize circulating current principle. Such types of protection are generally used for transformers of rating exceeding 2 MVA.

How many types of protection are there in a transformer?

No.	Fault Type	Protection used
1.	Primary winding Phase-Phase fault	Differential; Overcurrent
2.	Primary winding Phase-Earth fault	Differential; Overcurrent
3.	Secondary winding Phase-Phase fault	Differential
4.	Secondary winding Phase-Earth fault	Differential; Restricted Earth Fault (REF)

What is percentage differential protection of transformer?

Definition: The percentage differential relay is defined as the relay that operates on the phase difference of two or more similar electrical quantities. It is the advanced form of differential protection relay. The only difference between them is the restraining coil.

What is IS1 and IS2 in differential protection?

Relay Parameter Setting IS1: The basic differential current setting. K1: The lower percentage bias setting. IS2: The bias current threshold setting.

How is transformer differential protection calculated?

Application Example on Transformer Differential Protection Calculation

E87 = Y.
W1CT = Y.
W2CT = Y.
CTR1 = 80.
CTR2 = 240.
MVA = 33.
ICOM = Y.
W1CTC = 0.

How does a differential protection relay work?

Definition: The relay whose operation depends on the phase difference of two or more electrical quantities is known as the differential protection relay. It works on the principle of comparison between the phase angle and the magnitude of the same electrical quantities.

Which CT is used in differential protection?

The PS class CT is special protection class CT. Both the PS class CTs used for differential protection have the identical saturation characteristics and their knee point voltage are the same. The designer takes the data like lead resistance,relay burden and system fault level from user before design of PS class CT.

What are the applications of differential protection?

Differential protection is a fast and selective method of protection against short-circuits. It is applied in many variants for electrical machines, trans-formers, busbars, and electric lines.

Where Buchholz relay is used?

Buchholz relays have been applied on oil-filled power and distribution transformers at least since the 1940s. The relay is connected to the oil piping between the overhead conservator tank and the main oil tank of a transformer.

What are disadvantages of differential protection?

The Differential Protection of Transformers is also known as Merz-Price protection for the transformer. ... The differential scheme described suffers from the following drawbacks:

Unmatched characteristics of CTs.
Ratio change as a result of tapping.
Magnetizing inrush current.

What is the drawback of differential protection?

Difficulties of differential protection: (1) Saturation of CT magnetic circuit during short circuit condition: Due to these causes the relay may operate even for external faults, the relay may lose its stability for through faults.

Which type of construction is used for differential protection?

Translay scheme is mainly applied for differential protection of feeders. Here, two sets of current transformers have connected either end of the feeder. Secondary of each current transformer is fitted with individual double winding induction type relay.

What is a Buchholz protection?

The Buchholz protection is a mechanical fault detector for electrical faults in oil-immersed transformers. The Buchholz (gas) relay is placed in the piping between the transformer main tank and the oil conservator. The conservator pipe must be inclined slightly for reliable operation.

What are the 3 types of transformers?

Depending on the Power rating and specification, Power transformers can further be classified into three categories: Small power transformer, Medium Power transformers, and the Large power transformers.

What is OSR in transformer?

The protective Oil Surge Relay (OSR) is used to protect the malfunction developed inside the On Load Tap Changer (OLTC). It is installed in the pipe between OLTC head and oil conservator.

What is the CT ratio?

The CT ratio is the ratio of primary current input to secondary current output at full load. For example, a CT with a ratio of 300:5 is rated for 300 primary amps at full load and will produce 5 amps of secondary current when 300 amps flow through the primary.

Why do we use slope in differential protection?

The slope characteristic provides high sensitivity when low levels of current are flowing in the zone of protection but has less sensitivity when high levels of current are flowing and false differential current due to current transformer (CT) saturation is more likely.