Potential Transformer

Potential Transformer

A voltage transformer, also known as a potential transformer, is a type of instrument transformer used to measure and transform high voltage levels into manageable, low-voltage values suitable for monitoring and controlling devices. Its primary function is to repeat the fundamental voltage waveform while maintaining the phase connection.

Potential transformers are constructed with a main winding connected to the high voltage side of the circuit and a secondary winding connected to the low voltage side of the circuit. The ratio of turns between the main and secondary winding determines the transformation ratio of the potential transformer. This ratio permits precise voltage monitoring and the application of electrical system protection measures.

Construction

The potential transformer is built with a high-quality core that runs at a low flux value, resulting in a low magnetizing current. The transformer's terminals must be designed such that the voltage rating variations with load, as well as the phase shift between the output and input voltage, are as little as feasible.

The primary section has a considerable number of turns, whereas the secondary section has far less. A co-axial arrangement is employed in the potential transformer to minimise leakage reactance. Insulation costs are also decreased by dividing the major piece into particular sections, which minimizes the insulation between the layers.

 

Working of Potential Transformer

the voltage to be measured is linked between the potential transformer phase and ground in the power circuit. That is, the main winding of the potential transformer is linked to a high voltage circuit, while the secondary winding is connected to a voltmeter. The two winding are magnetically connected and operate by electromagnetic induction due to mutual induction.

The voltage across the secondary winding is measured in proportion to the voltage across the primary winding using the  multi meter or voltmeter. Because of the potential transformer's high impedance, only a small current flows through the secondary winding, and it functions similarly to an ordinary transformer with no or low load.

The voltage induced in the secondary is quite low because the primary has more turns than the secondary, which has less turns. A typical low voltage voltmeter is used to measure the secondary voltage. We can determine the primary voltage using the transformer's turn ratio equation.

VP/VS = NP/NS

 

Where

Primary Voltage = VP.

Secondary Voltage = VS.

Number of Primary Turns = NP

No. of Secondary Turns = NS

There is virtually little current flowing through the secondary windings of the PT because of the voltmeter's extremely high impedance. The PT has very low VA ratings of only 200 VA for the same reason.

Types of Potential Transformers

• Protection voltage transformers
• Metering voltage transformers

Pros

• When employing the capacitive potential transformer, it is very useful for measuring extremely high voltages.
• A regular voltmeter is capable of measuring extremely high voltages thanks to a potential transformer.
• Electrical separation between the voltmeter and the high voltage line provides protection.

Cons

• Only AC can be measured using it; high voltage DC is not allowed.
• They are more expensive than a regular transformer.

Applications Potential Transformer 

• Typically found in relay and metering circuits.
• Applications include power line carrier communication circuits.
• Electrically used in protective systems
• Used to keep feeders safe.
• Used in generators to shield the impedance.
• It is used to synchronize generators and feeds.
• Used as voltage protection transformers

 

Current Transformer

Current Transformers: Working Principles and Benefits

Current Transformers - A current transformer, also known as a CT, is a device designed to reduce high currents from a power circuit to a safe and manageable level for measuring instruments or protection relays. It generates an isolated secondary current proportional to the primary current passing through the conductor.

Line Conductor acting as primary 

Current Transformer Connections

Types of Current Transformers

Current transformers are classified into two types: wound primary and toroidal. Toroidal CTs have a closed-loop core through which the primary conductor is routed, whereas wound primary CTs have a primary winding through which the real current passes.

Working of Current Transformers

Winding and the Core

CT are made up of a high-permeability core that allows for efficient magnetic flux coupling. The core is often composed of silicon steel, ferrites, or amorphous alloys. Both primary and secondary windings are found around the core. The primary winding carries the real current to be measured or protected, while the secondary winding generates a proportional current to the primary current.

The Electromagnetic Induction Phenomenon

Current transformers work on the basis of electromagnetic induction. A magnetic field is created around the core as current flows through the primary winding. According to Faraday's law of electromagnetic induction, this magnetic field produces a current in the secondary winding.

Current Transformation Ratio

The link between main and secondary currents is determined by the CT's current transformation ratio (CTR). It is a key characteristic for precise measurement and protection and is stated as the ratio of primary current to secondary current.

Benefits of Using Current Transformers

Accurate Current Measurement - Current transformers give exact and dependable current measurements, making them essential in industries such as power generation, transmission, and distribution.

Instrumentation and Metering - CTs are essential in electrical instrumentation and metering, allowing for accurate invoicing and energy management.

Relay Protection and Fault Detection - CTs are used in power systems for protective relay applications. They aid in the detection of abnormal circumstances such as short circuits or over currents and initiate protective steps to protect equipment.

Energy Management and Efficiency - CT  aid in successful energy management by providing data on load profiles and usage patterns, allowing informed decisions to be made to increase energy efficiency.

Ground Fault Protection - CT help to defend against ground faults by detecting leakage currents and ensuring prompt disconnection to prevent electric shocks and fires.

Personal and Equipment Safety - CT improve both human safety and the longevity of electrical equipment by enabling accurate current measurements and rapid fault identification.

Applications of Current Transformers

1.    Power Transmission and Distribution

2.    Industrial Processes and Machinery

3.    Renewable Energy Systems

Final Outcome 

Current transformers are small yet essential components of modern power systems. Their functioning principles and benefits are applicable to a wide range of businesses, assisting with accurate measurements, protection, and effective energy management. We can continue to push improvements in electrical engineering and pave the road for a safer and more sustainable energy future by knowing how current transformers work and exploiting their powers.

Earth fault relay

Earth Fault Relays: Principles and Operation 

Earth Fault Relay:

An Earth Fault Relay, also known as an Earth Leakage Relay or Ground Fault Relay, is a protection device used in electrical systems to detect and respond to earth faults. An earth fault arises when an unintentional connection is made between an electrical conductor and the earth (ground). This can occur as a result of insulation failure, equipment malfunction, or unintentional contact with conductive objects. Earth faults are extremely dangerous since they can cause electric shock, equipment damage, and even fires.

 

Principle of Earth Fault Relay:

The Earth Fault Relay principle is based on Kirchhoff's current law, which asserts that the total current entering a node (or point) in an electrical circuit equals the total current exiting that node. The sum of all currents at every node should be zero in an ideal case, but in the presence of an earth fault, a portion of the current leaks to the ground, generating an imbalance.

This approach is used by Earth Fault Relays to detect such imbalances. They measure the current flowing through the electrical system's live (phase) and neutral conductors. The currents in both conductors are balanced under typical conditions, resulting in a net current of zero at the relay. However, if an earth fault occurs, the relay will detect the leaking current and trip, isolating the defective circuit.

 

Operation of Earth Fault Relays:

Let's go over the fundamental operation of Earth Fault Relays step by step:

 

Step 1: Current Measurement: Using current transformers (CTs), the Earth Fault Relay continually measures the currents in the live and neutral wires. These CTs reduce the current to a level adequate for the internal circuitry of the relay.

Step 2: Current Situation Analysis: The currents in the live and neutral wires are compared by the relay. If the two currents are equal or nearly equal (within a predetermined range), the relay believes the system is running normally and there is no earth fault.

Step 3: Imbalance Detection: When an earth fault occurs, a portion of the current spills to the ground. This causes a current imbalance between the live and neutral conductors. This imbalance is detected by the relay, which indicates the presence of an earth fault.

Step 4: Tripping and Alarm: When an earth fault is detected, the Earth Fault Relay sends a trip signal to the circuit breaker or contactor, isolating the problematic component of the electrical system. It may also activate an audible or visual alarm to notify maintenance staff of the malfunction.

Step 5: System Restoration: After repairing the earth fault and replacing or repairing the broken component, the relay can be manually reset to restore power to the isolated portion.

 

Types of Earth Fault Relays:

Earth Fault Relays are classified into several varieties, each with its own set of applications and characteristics. Some examples of frequent types are:

Zero Sequence Earth Fault Relay: This sort of relay is sensitive to the vector sum of all phase and neutral currents. It can identify earth faults in unbalanced load systems as well as single-phase earth faults.

Restricted Earth Fault Relay: As the name implies, this relay is intended to work only in one zone of the electrical system. It offers selective protection, detecting earth faults only inside a preset zone.

High-set Earth Fault Relay: This relay is employed in systems that are subject to high fault currents. It operates at a higher threshold to detect serious earth faults that regular relays may miss.

Low-set Earth Fault Relay: This relay is intended for low-fault-current systems. It detects even slight earth faults at a lower threshold.

 

Applications of Earth Fault Relays:

Earth Fault Relays are used in a variety of industries and electrical installations, including:

Residential Buildings: They are used to safeguard electrical circuits in homes and apartments against earth faults, assuring occupant safety.

Industrial Plants: Earth fault relays are critical in preventing accidents and equipment damage in industrial environments where electrical systems can be complicated and powerful.

Power Plants: These relays are used in power plants to detect and isolate earth faults, minimizing downtime and preserving system integrity.

Transportation Systems: Earth Fault Relays are used in railway and metro systems to assure the safe and reliable operation of electrical equipment.

Renewable energy systems are required in solar and wind power plants to protect the equipment and employees from earth faults.

 

Final Outcome:

Earth Fault Relays are critical components in modern electrical systems because they protect against earth faults and improve safety. These relays respond to faults quickly by continually monitoring and detecting imbalances in current flow, reducing potential risks and decreasing downtime. Earth Fault Relays are getting more sophisticated and reliable as technology advances, further enhancing their role in maintaining the safety and efficiency of electrical installations across numerous sectors.

Auxiliary Contactor

The Part of Auxiliary Contactors in Electrical Systems

 

Auxiliary Contactor- One switch can control another switch (often a larger switch) thanks to an auxiliary contactor. A standard (low-power) relay that is built like a "power" contactor and used in combination with another contactor is known as an auxiliary contactor. The set of contacts designated as "low voltage" is typically marked as such.

Auxiliary contacts are included in the control circuit and provide for a variety of functions. The auxiliary contacts can be either open or closed. When the contractor is de-energized, normally open are open. Normally, closed and open are diametrically opposed.

Some are employed in the controls to seal in or keep the main contactor closed after your finger is removed from the start button. Some allow start coils to remain in the circuit until a particular period or current is attained after beginning. Some contacts feature indicator lamps and remote motor status indications.

As a result, the primary connections supply electricity to the motor. Auxiliary contacts are utilized in motor controllers.

 

Distinction between an auxiliary and a power contactor

The main contactor is commonly a power contactor. It can withstand loads of up to 600 Amp. Auxiliary contactors, on the other hand, are only meant to switch currents of up to 10 Amp. A standard (low-power) relay that is built like a "power" contactor and used in combination with another contactor is known as an auxiliary contactor.

This is to emphasize that it is not used to switch loads, but rather has an activation/deactivation or control function.

Auxiliary contactors are used to connect and disconnect circuits (for example, to regulate power contactors).

Typically, auxiliary contactors have no primary connections and only auxiliary contacts.

Types of Auxiliary contactors

1.     Normally open

2.     Normally closed

Function of auxiliary contact block

The control and auxiliary circuits are operated via the auxiliary contact blocks. Auxiliary contact block types for common industrial settings: - Front-mounted, immediate CA4 1 or 4-pole blocks with NO and NC connections - Front-mounted, 1-pole CC4 block with N.O.

Auxiliary Contactor Applications

1) Circuits for motor control and starters

2) Building Automation and Lighting Control

3) Automation of Industrial Processes

 

Final Outcome - Auxiliary contacts serve a broad range of functions for motor-driven equipment and electrical professionals in the area of safety and protection against electrical problems

Thermal overload relay

Protecting Motors with Thermal Overload Relays: How They Work and Why They are Essential

Electrical motors are important in a wide range of sectors because it power multiple equipment that keep the industry running. For efficient operations and cost-effectiveness, it is important to ensure the reliability and dependability of these motors. The thermal overload relay is one of the important part that shields against damage and failure to motors. We will study the internal workings of thermal overload relays below, as well as their significance and the reasons why they are important for protecting motors.

Thermal Overload Relays

An electro mechanical safety device called a thermal overload relay is used to keep track of the winding of an electric motor's temperature. relay main purpose is to keep the motor from overheating, which can have detrimental effects including damaged insulation, burnt-out motors, or even fire threats.

1 Working of Thermal Overload Relays

A thermal overload relay's operation is based on the heating effect brought on by the current flowing through the motor's windings. A bimetallic strip or bimetallic element is attached to a collection of contacts to make up the relay. The bimetallic strip keeps its original shape and stays cool while the motor is operating normally, keeping the contacts closed. But when the motor runs, heat is produced by the current flowing through the winding. The increased current causes a similar rise in temperature when the motor is under an overload condition. Due to its various coefficients of thermal expansion, the bimetallic strip heats up along with the temperature and begins to bend. The contacts finally open as a result of this bending motion, interrupting the circuit and severing the motor's connection to the power source.

2 Distinguishing Circuit Breakers from Thermal Overload Relays

Circuit breakers and thermal overload relays both provide motor safety, although their functions are different. Thermal overload relays are designed to monitor the temperature of the motor and are sensitive to the gradual accumulation of heat brought on by protracted over current conditions. 

Thermal Overload Relays: Their Value

Let's examine why thermal overload relays are crucial for motor protection in various applications.

1 Preventing Overheating of the Motor

One of the most frequent causes of motor failures is motor overheating. Continuous overheating can cause insulation to deteriorate, which decreses  the life of the motor. As a safety measure, thermal overload relays turn off the power to the motor when the temperature exceeds a dangerous point, preventing damage and increasing the motor life.

2 Preventing Expensive Downtime

For industries, motor failures can mean expensive downtime that reduces output and costs money. plants can reduce the unplanned motor failures and lower the frequency of maintenance or replacement by adopting thermal overload relays, which saves both time and money.

3 Providing Safety

Electrical fires could also break out as a result of motor overheating, which can provide major safety issues. By cutting off the power when the motor reaches safe temperature thresholds, thermal overload relays are essential in preventing such risks.

4 Safeguarding Costly Equipment

Industrial motors costly to repair or replace, especially those found in large scale machines. A thermal overload relay serves as an insurance policy, guarding against damage to these expensive.

How to Choose the Best Thermal Overload Relay

To provide sufficient protection and top performance, the suitable thermal overload relay must be chosen for a certain motor application. Some important points must be taken into account throughout the selection process

 

1 Full Load Current and Motor Rating

To choose a thermal overload relay with the proper current range and trip class, you must be aware of the motor's power rating and full load current.

2 Outside Temperature 

Due to the potential impact on the motor's heating properties, consider the ambient temperature of the operating environment. Some thermal overload relays have mechanisms for compensating for ambient temperature to offer precise protection no matter the environment. 

3 Trip Time Modification

Verify the thermal overload relay's ability to alter the travel time. Specific trip times may be needed for different applications to account for different motor loads and speeds. Verify the thermal overload relay's ability to alter the travel time. To account for varied motor loads and starting circumstances, different applications could need distinct trip timing conditions.

Final Outcome 

In order to prevent motors from overheating and to maintain their continuing effective performance, thermal overload relays are essential.

 

buchholz relay

Relay - Relay is a simple electro mechanical device or switch which is use to make the circuit connect and disconnect like a switch but in normal switch operate in manually but in a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit as per the requirement. 

The relay operates on the electro-magnetic induction principle.

Relay types - Relay is classified into different part as per it's function, structure and it's use.. 

• Thermal
• Differential
• Distance
• Automotive
• Frequency
• Polarized
• Rotary
• Sequence
• Moving Coil
• Buchholz
• Electromagnetic
• Latching
• Electronic
• Non-Latching

Buchholz Relay definition-  it's an gas operated type of relay which is used in oil impressed transformers to protect transformers form internal faults.

It's placed between the main tank of the transformer and conservator tank.

It is not used in small transformer because of  its pricing issue.

 

Buchholz Relay working Principle- The temperature of the oil rises when a fault occurs inside the transformer. The main tank's oil evaporates and turns into gas. The magnitude of the fault that occurs inside the transformer determines the generation of flu gas. Internal failure occurs in the transformer due to either insulation breakdown between the winding or a weak initial contact between the winding.

 

Buchholz-relay -The arc is caused by the defect, which raises the temperature of the oil. The oil evaporates and rises in the atmosphere. Before tripping the transformer and disconnecting it from the main supply source, the Buchholz relay detects the failure and warns the staff.

  

Construction of Buchholz Relay - Buchholz relays are made out of an oil-filled chamber. In the chamber, there are two hinged floats, one at the top and one at the bottom. A mercury switch is attached to each float. The upper float's mercury switch is connected to an alarm circuit, while the lower float's mercury switch is connected to an external trip breaker to cut the supply source.

1) Two hinged floats

2) Two mercury switches 

3) Release cock

4) Test cock

5) outer enclosure 

Construction of Buchholz Relay

# The minimum operating time of the relay is very minimum  (0.1 seconds).

 

Limitations of Buchholz Relay- There are some limitations of the buchholz relay.

1) the relay is only used in oil-immersed transformers.

2) it's work only for internal faults.

3) Relay response time is very high.

Testing and Maintenance of buchholz Relay

By forcing air into the float chamber to remove the liquid and make the floats fall, it is typically able to test the float operators. By turning a rod, or portable lever, attached on the relay's housing, the baffle plate can be inspected. By measuring the resistance with a typical multi meter, the condition of the electrical switches themselves can be determined.

Advantages of Buchholz Relay -

1) Operation is reliable. 

2) Simple in construction

Disadvantages of Buchholz Relay

1) only used for oil immersed transformers. 

2) only used for internal faults.