Headline :- “Power Protection 101: The Single Phase
Preventer’s Essential Guide”
Abstract
This abstract explores the interconnected aspects of a single-phase preventer, electrical supply, and
electrical motor. It delves into the significance of a single-phase preventer in safeguarding electrical
motors from potential damage due to phase imbalances. The discussion encompasses the role of a
reliable electrical supply in ensuring optimal motor performance and the implications of a single-phase
preventer in maintaining operational integrity. Additionally, the abstract touches upon the broader
context of these components within electrical systems, emphasizing their collective importance in
promoting efficiency and longevity.
Electrical supply basics
What is Electrical supply?
Electrical supply refers to the provision of electrical power to homes, businesses, and other facilities for
various purposes such as lighting, heating, cooling, and powering appliances and machinery. It involves
the generation, transmission, distribution, and utilization of electricity through a network of power
plants, substations, transformers, power lines, and electrical infrastructure. Electrical supply systems
vary in complexity and scale, ranging from local distribution networks to regional or national grids.
Types of supply
1. Single phase supply
2. Three phase supply
3. DC supply
Why three phase AC supply is used rather than DC supply?
Three-phase AC supply is preferred over three-phase DC supply due to its ease of generation and
transmission, cost-effectiveness, flexibility in voltage control, compatibility with induction motors,
safety, reduced corrosion risks, and established infrastructure.
Why three phase supply is generally used over single phase supply?
Three-phase supply is generally preferred over single-phase supply for several reasons:
1.
2.
3.
4.
Power Delivery
Balanced Loads
Motor Operation
Cost Efficiency
5. High Power Requirements
What are disadvantages of three phase supply?
Some disadvantage of three phase supply are as follows:1.
2.
3.
4.
5.
Complexity
Higher Initial Cost
Limited Residential Use
Voltage Imbalance
Safety Concerns
6. Limited Availability
Where should we use single phase or three phase?
Single-phase supply is typically used in residential settings, small businesses, and light commercial
applications where power demand is relatively low and simplicity of installation is preferred.
Threephase supply is more suitable for industrial, commercial, and high-power applications where
efficiency, balanced loads, and reliable power distribution are essential. It is commonly used in factories,
large commercial buildings, industrial machinery, and heavy-duty equipment due to its ability to deliver
higher power output and smoother operation.
Electrical motor overview
An electrical motor is a device that converts electrical energy into mechanical energy. It operates based
on the principles of electromagnetism, where the interaction between magnetic fields and electric
currents produces motion.
Electrical motors are used in various applications, from powering household appliances to driving
industrial machinery and vehicles.
They come in different types, including AC motors (alternating current) and DC motors (direct current),
each suited for specific purposes and operating conditions.
Classification of electrical motor
Maintenance of electrical motors
It is divided into
1) Routine Maintenance (Daily/Weekly)
Routine maintenance of electrical motors involves regular inspections for signs of wear, cleaning to
remove dust and debris, and ensuring proper lubrication of moving parts. Additionally, monitoring
temperature and voltage fluctuations helps prevent overheating and extends the motor’s lifespan.
2) Scheduled Maintenance (Monthly/Quarterly)
Scheduled maintenance for electrical motors includes regular inspections for wear, cleaning to remove
debris, and lubrication of moving parts, alongside monitoring temperature and voltage fluctuations to
prevent overheating and ensure longevity. Adhering to these practices enhances motor efficiency and
reduces the risk of unexpected failures.
3) Preventive Maintenance (Semi-Annually/Annually)
Preventive maintenance for electrical motors entails regular inspections, lubrication of moving parts,
and timely component replacements to prevent failures and minimize downtime. These proactive
measures enhance motor reliability, extend its lifespan, and reduce operational costs in the long run.
4) Comprehensive Maintenance (Biennially/Every Few Years)
Comprehensive maintenance encompasses thorough inspections, systematic cleaning, lubrication, parts
replacements, and performance evaluations to ensure optimal functionality and longevity of equipment.
By addressing all aspects of upkeep, comprehensive maintenance minimizes downtime, reduces the risk
of breakdowns, and maintains peak operational efficiency.
What problems arrive in Three phase motor
Some example of faults arriving in motor are :Stator Faults: Such as short circuits or open circuits in windings, leading to uneven torque and
overheating.
Rotor Faults: Including broken rotor bars or end rings, resulting in abnormal vibration and reduced
torque.
Grounding Faults: Such as insulation breakdown or ground faults, which can lead to safety hazards and
motor malfunctions.
Voltage imbalance
Interturn fault
Mechanical fault
Single phasing ( the type of fault which is addressed to the topic single phase preventer)
Single phasing also described as one phase of motor of three phase gets disconnected due to starting
motor with the help of starter.
This happens due to the burning out of one fuse out of three fuses. Generally, this happens in the
operation of star- delta starter or Auto-transformer starter used to start the motor due to defective
contact in ‘run’ side of starter.
This can lead to various problems such as reduced torque, overheating, increased current draw, and
potential damage to the motor windings and other components.
The ABC of single phase preventer :- A deep dive into single phase preventer
fundamentals
Why is single phase preventer used?
Single phase preventer is used to prevent single phasing fault occuring in 3 phase motor which is
covered above.
What is the Effect of single phasing?
Effect on 3-phase heating loads: The heat produced by heating element is decreases around 50% but it
does not harm the equipment.
Effect on three-phase motors:
Single-phasing in three-phase motors causes damaging effects. During starting, lack of a proper rotating
magnetic field prevents motor initiation, leading to high current draw and overheating of windings. If
single-phasing happens during running, the motor might continue running but with increased current
draw, risking winding burnout due to overheating.
Causes of single phasing
1.
2.
3.
4.
One of the fuse may blown off
Line wires are broken
Relay contacts may be damage
Contact joints are not conducting properly
Single phase preventer
A single-phase preventer is also known as a phase failure relay or a phase sequence relay. These devices
monitor the electrical supply to motors and machinery, detecting any abnormalities such as phase loss
or incorrect phase sequence. When a fault is detected, the preventer interrupts the power supply to
prevent damage to the equipment and ensure safe operation.
Types
1. Voltage sensing single phase preventer
2. Current sensing single phase preventer
3. Mechanical single phase preventer
Voltage type
Phase sequence in a three-phase AC supply dictates the order in which phase voltages reach their
maximum values. Positive sequence occurs in a clockwise direction, while negative sequence goes
counterclockwise. Single phasing or phase reversal can overlay a negative sequence, posing risks.
Voltage sensing single-phasing preventers employ resistance-capacitance or resistancecapacitanceinductor networks to filter out negative sequences, safeguarding equipment by deenergizing relays upon detection.
Current type
The current sensing type single phasing preventer operates on the principle of equal currents with
balanced loads developing secondary voltage on CT (current transformers).
These secondary of current transformer are connected to ADD and the added signal is rectified, filtered
and sensed and applied to operate a relay which use to close the NVC (no voltage coil) circuit of the
starter.
In normal operating condition motor starter contact connection is always in closed condition
Mechanical type
Mechanical type single-phasing preventers employ bimetal relays or phase failure relays. Bimetal relays,
though slow and unreliable, interrupt the circuit similarly to overload relays. In contrast, phase failure
relays utilize coils between two lines of the three-phase supply to create a rotating magnetic field. This
field turns a copper disc, triggering a toggle mechanism to disconnect the motor if any one phase fails,
thereby safeguarding the motor from single-phasing damage.
Construction
wiring diagram
Main parts
1. Control coil,
2. Negative sequence filter,
3. Contactors,
4.
5.
6.
7.
Normally closed NC contact,
Normally open NO contact,
C.T.S.,
Thermal relay.
Working
In Fig. 1 the parts are shown connected to the protective circuits and motor. The preventive circuit is
connected in secondary of C.T. and R.Y.B. lines act as primaries of the CT. The negative sequence filter is
shown connected. The output of this lifter is fed to a level detector. This sends the tripping command to
the starter and NC contact gets opened and contactors get opened, stopping the motor as it is disconnected from the supply R.Y.B. This type of preventer is generally used for small/medium capacity
motors.
Wave diagram of single phasing fault
In a diagram illustrating single phasing, one of the three phases in a three-phase
electrical system is shown as disconnected or lost. The remaining two phases
continue to supply power to the motor, causing an imbalance in the system. This
imbalance leads to increased current flow in the remaining phases, resulting in
overheating and reduced motor performance. Detecting and rectifying single
phasing promptly is essential to prevent motor damage and ensure the safety and
efficiency of the electrical system.
Single phasing actual diagram
Under normal condition
Under fault condition
Percentage of causes of motor failure
Failure
Percentage
Overload
30 %
Contaminants
19%
Single phasing
14%
Bearing failure
13%
Old age
10%
Rotor failure
5%
Miscellaneous
9%
Against which faults does it offers protection?
Single phase preventer offers protection against various fault such as
1. Single phasing
2. Unbalanced voltage
3. Phase reversal
Case study
In 2005, the Cooper Bussmann facility in St. Louis, Missouri experienced a power issue called single
phasing for over two hours. They had over 100 motors running at the time. Luckily, even though the
exact cause wasn’t disclosed, the motors were well-protected. Each motor had safety features like
overload relays and fuses. Despite the power problem, none of the motors were damaged, and the
facility got back to normal after replacing fuses and resetting overload relays.
Conclusion:
In conclusion, the seamless integration of single-phase preventers within electrical systems significantly
enhances efficiency and promotes the longevity of electrical motors. Their pivotal role in safeguarding
motors from phase imbalances ensures operational integrity, minimizing downtime and enhancing
overall productivity across diverse industrial applications.
Observation:
Single-phase preventers serve as critical components in industrial electrical systems, offering essential
motor protection against single-phasing situations. By monitoring electrical phases and interrupting
power during phase failures, they prevent potential damage to motors, thereby sustaining operational
reliability.
Advantages of Single Phase Preventer:
The advantages of single-phase preventers are multifaceted. They provide cost savings by preventing
motor damage, thereby reducing repair and replacement expenses. Their ease of installation and
integration into existing systems make them a practical and economical choice for motor protection.
Additionally, they enhance system reliability by ensuring uninterrupted motor operation, particularly in
critical applications such as pump systems and compressor units.
Disadvantages of Single Phase Preventer:
However, single-phase preventers have inherent limitations. They primarily address single-phasing
situations and may not mitigate other potential electrical issues such as overvoltage, undervoltage, or
phase sequence faults. Their effectiveness relies heavily on a stable and continuous power supply,
making them susceptible to disruptions during power outages or fluctuations. Moreover, regular
maintenance is essential to uphold their reliability and effectiveness over time.
Applications of Single Phase Preventer:
Single-phase preventers find widespread applications across various industries, including pump systems,
compressor units, conveyor belts, and industrial machinery. They are particularly crucial in
environments where motor operation is critical for maintaining workflow and preventing costly
downtime.
This organization provides a comprehensive overview of single-phase preventers, encompassing their
benefits, limitations, and diverse industrial applications.
References
Website
1) https://www.eaton.com/content/dam/eaton/products/electrical-circuitprotection/fuses/solution-center/bus-ele-tech-lib-motor-single-phasing-voltageunbalance.pdf
2) https://www.ijspr.com/citations/v34n3/IJSPR_3403_1923.pdf
3) https://forumelectrical.com/working-principle-of-single-phase-preventer-relay/
4) https://instrumentationtools.com/working-principle-of-single-phase-preventer-relay/
5) https://omgfreestudy.com/single-phasing-preventer/
6) https://industrialgyan.com/single-phase-preventer/
7) https://www.jetir.org/papers/JETIR2202429.pdf
8) https://www.marineinsight.com/marine-electrical/single-phasing-in-electrical-motors-causeseffects-and-protection-methods/
9) https://www.cyberpowersystems.com/blog/single-phase-vs-3-phase-power-protection/
10) https://www.rowse.co.uk/blog/post/three-phase-and-single-phase-explained
11) https://blog.tripplite.com/single-phase-vs-three-phase-power-explained
12) https://sinovoltaics.com/learning-center/basics/single-phase-power-supply/
13) https://en.m.wikipedia.org/wiki/Electric_motor#:~:text=An%20electric%20motor%20is%20an
,applied%20on%20the%20motor’s%20shaft.
14) https://www.britannica.com/technology/electric-motor
15) https://www.iqsdirectory.com/articles/electric-motor.html
16) https://www.parvalux.com/what-are-the-different-types-of-electric-motors/
17) https://electricalworkbook.com/electric-motor-diagram-working/
18) https://www.rbaker.co.uk/electric-motor-maintenance/
19) https://www.pdfsupply.com/blog/index.php/2023/08/20/the-importance-of-maintenancein-motor-systems/
Books
1) Tech knowledge publications
Switch gear and protection
Author :- S . M . Chaudhari & M . A. Chaudhari
2) Tech knowledge publications
Industrial AC Machines
Author :- J.S. Khatre