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Examoogle • User • info@examoogle.com • EE-2024-8821
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The range can be increased by using which of the following instrument?
Energymeter
Voltmeter
Ammeter
Current Transformer
Current Transformer
Quick Summary: A Current Transformer (CT) is an instrument transformer used to step down high currents to a standardized low value, typically 5A or 1A, which allows for the measurement of high-magnitude currents using low-range ammeters. By changing the turns ratio, the effective range of the connected measurement instrument is significantly increased.
A Current Transformer (CT) is an instrument transformer used to step down high currents to a standardized low value, typically 5A or 1A, which allows for the measurement of high-magnitude currents using low-range ammeters. By changing the turns ratio, the effective range of the connected measurement instrument is significantly increased.
I2=I1×N2N1 — Secondary current relationship
K=N1N2 — Transformation ratio of the CT
The CT operates on the principle of electromagnetic induction similar to a standard transformer. The primary winding, connected in series with the high-current circuit, has few turns, while the secondary winding has a large number of turns. According to the transformer law N1I1=N2I2, the secondary current I2 is proportional to the primary current I1 scaled by the turns ratio N1/N2, allowing a low-range ammeter to measure a scaled version of the primary current.
CTs isolate measurement devices from high-voltage primary circuits.
The secondary of a CT should never be open-circuited while the primary is energized to prevent high induced voltages and core saturation.
Standard secondary current ratings are typically 1A or 5A.
Allows measurement of very high currents using standard low-range instruments.
Provides electrical isolation between the high-voltage circuit and the secondary metering circuit.
Reduces the cost of metering infrastructure.
Risk of high voltage induction if the secondary circuit is opened.
Introduces phase angle errors and ratio errors in high-precision applications.
Electrical power grid metering.
Protection relaying for overcurrent conditions.
Industrial energy monitoring systems.
Option B (Voltmeter) uses Potential Transformers (PT) to extend its range.
Option C (Ammeter) without a CT is limited to its own internal shunt capacity.
CT secondary terminals must be shorted before disconnecting the ammeter.
D is correct — A Current Transformer (CT) is specifically designed to step down high primary currents to a range suitable for measurement by standard ammeters, thereby increasing the effective measurement range.
Always remember: CTs are connected in series with the line, and their secondaries must be kept closed to avoid high induced EMFs due to core flux saturation.