How does transformer differential protection work?

How does transformer differential protection work?

Differential protection works on the principle of Kirchhoff’s Current Law (KCL). This law states that the total sum of current flowing in to a node is zero. If the per unit primary side current is equal to per unit secondary side current, then KCL is verified and no fault is present in the transformer.

What are the difficulties associated with differential protection?

The differential scheme described suffers from the following drawbacks: Unmatched characteristics of CTs. Ratio change as a result of tapping. Magnetizing inrush current.

Where the differential protection is supremely used?

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 problems arising in differential protection in power transformer?

What are the problems arising in differential protection in power transformer and how are they overcome? 1. Difference in lengths of pilot wires on either sides of the relay. This is overcome by connecting adjustable resistors to pilot wires to get equipotential points on the pilot wires.

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.

How is transformer differential protection calculated?

Application Example on Transformer Differential Protection Calculation

1. E87 = Y.
2. W1CT = Y.
3. W2CT = Y.
4. CTR1 = 80.
5. CTR2 = 240.
6. MVA = 33.
7. ICOM = Y.
8. W1CTC = 0.

What is line differential protection?

An alternative principle for line protection that is quickly becoming the norm is differential protection. Differential protection is based on Kirchhoff’s laws, stating that all current into a network node shall add up to 0 in an ideal system.

Which type of relay is used for protection of feeders?

differential relay
The differential relay is used for the protection of the feeder, large busbars, etc.

What are the limitation of differential protection when applied to transformers?

There are some disadvantages in the voltage balance differential relay such as a multi tap transformer construction is required to accurate balance between current transformer pairs. The system is suitable for protection of cables of relatively short length otherwise capacitance of pilot wires disturbs the performance.

What is simple differential protection?

Introduction. Differential protection is a unit-type protection for a specified zone or piece of equipment. It is based on the fact that it is only in the case of faults internal to the zone that the differential current (difference between input and output currents) will be high.

What is 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.

What is percentage differential protection?

The percentage differential relay is designed to operate the differential current in terms of its fractional relation with actual current flowing through the circuit. It is used to protect the system under Current transformer saturation, unequal CT ratios, nuisance trip etc.

How to calculate the differential protection of a transformer?

Let us examine the response of our transformer differential protection on through fault conditions. Consider a single line-to-ground through fault as shown on the figure below. The currents seen by the relay are affected by the CT ratio and connection hence the values of the secondary currents before compensation.

Can a wye transformer be connected to a delta transformer?

For example, a delta wye transformer has a 30-degree phase angle difference between primary and secondary. Whether the delta leads wye or wye leads delta depends on the type of delta closing and is discussed in this article. Additionally, CTs could be connected in delta or wye which also could introduce phase angle errors.

What is the working principle of a differential protection relay?

This law states that the total sum of current flowing in to a node is zero. If the per unit primary side current is equal to per unit secondary side current, then KCL is verified and no fault is present in the transformer. This is the basic working principle of a transformer differential protection relay.

How to calculate differential protection setting for delta connected CTS?

Differential Protection Setting Calculations For Delta connected CTs, to obtain secondary current, use: (1.73) I PRI / CTR = I SEC Fault Types and Currents in Secondary Circuits Differential Protection Setting Calculations ƒDetermine all device burdens in secondary circuit – Relays, meters, instrumentation ƒDetermine lead burden