Usage and operation of CT and PT.

Experiment No: – 08

Aim of the Experiment: –

                                                        Usage and operation of CT and PT.

Apparatus Required: –

Sl. No.	Name	Specification	Quantity
1	Current Transformer (CT)	100A/5A	1 no.
2	Potential Transformer (PT)	11kV/110V	1 no.
3	Ammeter	(0-10) A	1 no.
4	Voltmeter	(0-230) V	1 no.
5	Load Resistance	(0-80) Ω, 5A	1 no.
6	Connecting Wires	PVC Insulated copper	As per required
7	Single-phase auto-transformer	5kVA, (0-300) V, 10A	1 no.

Circuit Diagram: –

Theory: –

                 Current Transformers (CTs) and Potential Transformers (PTs) are vital components in electrical power systems. They are used for measurement, protection, and control purposes.

Operation of CTs and PTs:

1. Transformers: CTs and PTs operate based on the principles of electromagnetic induction, similar to conventional power transformers. They consist of primary windings (connected in series with the current or voltage to be measured) and secondary windings (connected to measuring devices, relays, or meters).
2. Turns Ratio: CTs and PTs have a specific turns ratio, which determines the relationship between the primary and secondary currents or voltages. The turns ratio defines the transformation ratio between the primary and secondary values.
3. Accuracy Class: CTs and PTs have accuracy classes that specify their level of accuracy in transforming primary currents or voltages to secondary values. Accuracy classes are expressed as a percentage and indicate the maximum deviation from the true value.
4. Burden: CTs and PTs have a burden, which represents the impedance presented by the secondary circuit. It is important to ensure that the burden does not exceed the rated limits of the CT or PT to maintain accuracy and avoid damage.

Procedures: –

1. Connect all the apparatus as per circuit diagram.
2. Connect the CT and PT to their respective measurement devices (ammeter and voltmeter) using appropriate connecting wires. Ensure that all connections are secure and insulated.
3. Connect the CT to the ammeter and the load resistance.
4. Slowly vary the applied current to the circuit through the load resistance.
5. Observe and record the reading on the ammeter and see the relationship between the primary current and the secondary current measured by the ammeter.
6. Connect the PT to the voltmeter and the load resistance.
7. Slowly vary the applied voltage to the circuit across the load resistance.
8.  Observe and record the reading on the voltmeter and see the relationship between the primary voltage and the secondary voltage measured by the voltmeter.

Observation Table: –

For CT:

Sl. No	Primary Current (I1 in amps.)	Secondary Current (I2 in amps.)	% Errors= {(I1 – I2)/ I1 } * 100
1
2
3
4
5

For PT:

Sl. No	Primary Voltage (V1 in Volts.)	Secondary Voltage (V2 in Volts.)	% Errors= {(V1 – V2)/ V1 } * 100
1
2
3
4
5

Conclusion: –

    Written By Student.

For reference: –

Current Transformers (CTs):

1. Measurement: CTs are primarily used to measure high currents in power systems. They transform high primary currents into proportional secondary currents that can be easily measured by current meters, relays, or protective devices.
2. Protection: CTs play a crucial role in protective relaying schemes by providing current inputs for fault detection, current differential protection, overcurrent protection, and ground fault protection.
3. Instrumentation: CTs are used in power monitoring and metering applications, providing accurate measurements of current flow for billing, load management, and analysis.
4. Control: CTs can be used for feedback in control systems to monitor current levels and regulate the operation of devices such as motor starters, variable frequency drives, and power converters.
5. Safety: CTs enable safe measurement and protection by isolating high currents from metering and control circuits, reducing the risk of electric shock and equipment damage.

Potential Transformers (PTs): –

1. Measurement: PTs are used to step down high voltage levels to safe and measurable levels. They provide accurate voltage measurements for metering, monitoring, and control purposes.
2. Protection: PTs are essential in protective relaying schemes, providing voltage inputs for voltage-based protection functions such as overvoltage protection, undervoltage protection, and voltage control.
3. Instrumentation: PTs are utilized in power monitoring and metering applications, providing accurate voltage measurements for billing, load management, and analysis.
4. Control: PTs can be used for voltage regulation and control in electrical systems, allowing devices such as voltage regulators and tap changers to operate based on precise voltage measurements.
5. Safety: PTs isolate high voltages from metering and control circuits, ensuring the safety of personnel and equipment during voltage measurement and control operations.