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Examoogle • User • info@examoogle.com • EE-2024-8821
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Which is called rated burden of relay?
Voltage
Ampere
Power consumption
None of above
Power consumption
Quick Summary: The rated burden of a relay is defined as the power consumed by the relay coil at its rated current or voltage. It is expressed in Volt-Amperes (VA) for AC circuits to quantify the load imposed by the relay on the instrument transformers (CTs or PTs) supplying it.
The rated burden of a relay is defined as the power consumed by the relay coil at its rated current or voltage. It is expressed in Volt-Amperes (VA) for AC circuits to quantify the load imposed by the relay on the instrument transformers (CTs or PTs) supplying it.
S=V⋅I — Fundamental Power formula for burden
SCT=Irated2⋅Zrelay — Burden for overcurrent relays
A protective relay is connected to the secondary of a Current Transformer (CT) or Potential Transformer (PT). The relay coil acts as an impedance Z. The power consumed by this impedance is the burden, given by S=I2Z for overcurrent relays or S=V2/Z for overvoltage relays. Ensuring the relay burden remains within the rated capacity of the CT/PT is critical to avoid saturation and ensure measurement accuracy.
Burden is expressed in VA for AC and Watts for DC.
A lower relay burden is preferred to increase the accuracy of instrument transformers.
Excessive burden causes CT saturation and reduces the relay's sensitivity.
It is measured at a specified frequency (usually 50 Hz in India).
Helps in selecting appropriate CT/PT ratings.
Ensures compatibility between secondary equipment and instrument transformers.
Higher relay burden increases the heat dissipation in the relay coil.
High burden requires larger, costlier instrument transformers.
Switchgear protection design
Coordination of relays in power systems
Standard burden values are often specified by manufacturers at rated current (e.g., 1A or 5A).
Option A (Voltage) and Option B (Ampere) are independent parameters that, when multiplied, constitute the power (VA).
C is correct — Rated burden is the power consumption of the relay coil, expressed in Volt-Amperes (VA).
Always ensure the total connected burden of all relays on a CT secondary circuit does not exceed the CT's rated burden to prevent accuracy class degradation.