Differential Transformer Protection - 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 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.

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 is slope in differential relay?

Thus to prevent tripping on through fault we provide a slope so that Differential current increases as the Biasing current increases and Differential protection will operate if the slope exceeds a particular value (which can be set in the Relay).

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.

How does a Buchholz relay work?

How does a Buchholz Relay work? Whenever a minor fault occurs inside the transformer, heat is produced by the fault currents. The produced heat causes decomposition of transformer oil and gas bubbles are produced. These gas bubbles flow in upward direction and get collected in the buchholz relay.

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 a MHO relay?

Mho relay is a voltage restrained directional relay. Important Points: Reactance relay is suitable for the protection of a short transmission line because its operation is independent of arc resistance. The relay which is selected for a long transmission line should be less affected due to power swings.

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 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.

What is 0.2 S Class CT?

An 0.2s accuracy class means that the measurement has an error rate of 0.2% over a range of 20 to 120% of the nominal current (In) and at a specific accuracy above 1% of In. Wide dimensions choice Three models to allow through any primary conductor, cables or bar.

What are the different types of differential relay?

Differential Relay & Its Types - Current Differential & Percentage Differential Relay. The overcurrent relays are used for the protection of electrical equipment against fault currents. But this type of relay is not very sensitive as they cannot distinguish between overloads and minor fault conditions.

What is line differential protection?

Line differential protection is one of the most popular forms of transmission line protection. This type of protection is based on Kirchoff's current law, which states that the current flowing into a line must be equal to the current flowing out of the line.

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.

What is a 59 relay?

59 Overvoltage relay A relay that operates when its input voltage is more than a predetermined value. 60 Voltage or current balance relay A relay that operates on a given difference in voltage, or current input or output, of two circuits.

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.

How much percentage of winding is protected by differential protection?

The percentage of winding to be protected against phase to ground fault is 85%.

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.

What are the limitations of differential relay?

Disadvantages of Current Differential Relay: If the relay is very sensitive, then the small differential current flowing through the relay may cause it to operate even under no fault. Pilot cable capacitance causes incorrect operation of the relay when a large through-current.

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.