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Static Impedance Relay

An impedance relay measures the line impedance between its location and the point of fault by comparing the current (I) and voltage (V) signals. It produces positive torque from current and negative torque from voltage, with impedance calculated as Z=V/I. There are two main methods for static impedance relays - using an amplitude comparator that compares operating current I to restraining voltage V, or using a phase comparator that compares the phase angle between vectors (IZr + V) and (IZr - V), where Zr is the relay impedance setting. The phase comparator method realizes the impedance characteristic by ensuring the phase angle is less than ±90 degrees. Impedance relays are compact, robust

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3K views11 pages

Static Impedance Relay

An impedance relay measures the line impedance between its location and the point of fault by comparing the current (I) and voltage (V) signals. It produces positive torque from current and negative torque from voltage, with impedance calculated as Z=V/I. There are two main methods for static impedance relays - using an amplitude comparator that compares operating current I to restraining voltage V, or using a phase comparator that compares the phase angle between vectors (IZr + V) and (IZr - V), where Zr is the relay impedance setting. The phase comparator method realizes the impedance characteristic by ensuring the phase angle is less than ±90 degrees. Impedance relays are compact, robust

Uploaded by

Anonymous C9ZNFkrb6
Copyright
© © All Rights Reserved
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Impedance Relay

An impedance relay is kinds of relay which measure the line

impedance between the relay location & the point of fault.


Current produce = Positive torque
Voltage produce = Negative torque
Impedance, Z=V/I

Static Impedance Relay Using an


Amplitude Comparator

Fig: Static Impedance Relay Unit Using Amplitude Comparator

Description of Static Impedance


Relay
Rectifier bridge comparator is used to realize an
impedance relay characteristic. Since it is an amplitude
comparator, I is compared with V. I is an operating
quantity and V is the restraining quantity . As the
rectifier bridge arrangement is a current comparator, it
is supplied with the operating current Io and restraining
current Ir. Io is proportional to the load current I and
Ir is proportional to the system voltage V.

Static Impedance Relay Using a


Phase Comparator.

Fig: Phase diagram of showing V , I & voltage drop.

Static Impedance Relay Using a


Phase Comparator

Fig: Impedance diagram of static relay using a


phase comparator

Description of Impedance diagram


Now, a circle with radius Zr, is drawn, as shown in Figure. Since NM
is the diameter of the circle, No = Zr and vector NP = Zr + Z. The
angle between (Zr + Z) and (Zr - Z) is . if the point P lies within the
circle, is less than 90.If P falls outside the circle, is greater than
90. Thus, to realize an impedance characteristic, the phase angle
between (Zr + Z) and (Zr - Z) is to be compared with 90. If we
multiply these impedance vectors by I the resulting vectors are
I(Zr + Z) and I(Zr - Z)
or (IZr + IZ) and (IZr - IZ)
or (IZr + V) and (IZr - V)

Operational view of Impedance


Relay.

Fig: Impedance Relay using its operational view.

Realization of the characteristics.


Therefore, to realize an impedance relay characteristic
using a phase comparator, the phase angle , between
(IZr + V) and (IZr - V) is compared with 90. if is
less than 90 the point lies within the characteristic
circle (IZr + V) is the polarizing input and (IZr - V) is
the operating input.

Advantages of Impedance Relay


This construction is compact & robust.
It produce no vibrating torque.
It is less affected by DC transients.
It possesses high speed & sensitivity.
It gives a perfect circular characteristics.

Applications of Impedance Relay


Protection of transmission & sub-transmission lines at

220 kv, 132 kv, 66 kv, 33 kv. Sometimes they are also
used at 11 kv line.

Thank you

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