{"id":97743,"date":"2022-01-07T20:05:26","date_gmt":"2022-01-07T18:05:26","guid":{"rendered":"https:\/\/gahzly.com\/%d9%85%d8%a7-%d9%87%d9%88-%d8%a7%d9%84%d8%a7%d9%88%d9%81%d8%b1-%d9%84%d9%88%d8%af-%d8%a3%d9%86%d9%88%d8%a7%d8%b9%d9%87-%d9%88%d8%aa%d8%b7%d8%a8%d9%8a%d9%82%d8%a7%d8%aa%d9%87\/"},"modified":"2023-12-20T15:59:40","modified_gmt":"2023-12-20T13:59:40","slug":"what-is-an-overload-relay-its-types-and-applications","status":"publish","type":"post","link":"https:\/\/gahzly.com\/en\/\u0645\u0642\u0627\u0644\/what-is-an-overload-relay-its-types-and-applications\/","title":{"rendered":"What is an overload relay: its types and applications"},"content":{"rendered":"

What is an overload relay: its types and applications<\/span><\/span><\/strong><\/h1>\n

 <\/p>\n

\"WhatOverload is an electrical device used to protect an electric motor from overheating.<\/span><\/span><\/span><\/p>\n

It is therefore essential to have adequate engine protection.<\/span><\/span><\/span><\/p>\n

The electric motor can be started safely with the help of overload relays, fuses or circuit breakers.<\/span><\/span><\/span><\/p>\n

But this relay protects the motor while the fuse circuit breaker protects the circuit.<\/span><\/span><\/span><\/p>\n

More intentionally, fuses, as well as circuit breakers, are intended to detect excess current within a circuit<\/span><\/span><\/span><\/p>\n

, while the relay is intended to detect overheating in the event of an electric motor heating up.<\/span><\/span><\/span><\/p>\n

For example, it can troubleshoot overload without tripping the CB (circuit breaker)<\/span><\/span><\/span><\/p>\n

. One does not restore the other.<\/span><\/span><\/span><\/p>\n

This article discusses an overview of overload, its types and how it works.<\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

What is an overload relay?<\/span><\/span><\/h2>\n

Overload can be defined as an electrical device designed primarily to mimic the heating patterns of an electric motor<\/span><\/span><\/span><\/p>\n

, In addition to breaking up the current flow when the heat detector in the relay reaches a constant temperature.<\/span><\/span><\/span><\/p>\n

An overload can be designed using a coupled heater with generally closed connections that open when the heater gets too hot.<\/span><\/span><\/span><\/p>\n

The connections of this relay can be made in series as well as placed between the motor and the contactor itself to avoid restarting the motor on overload trips.<\/span><\/span><\/span><\/p>\n

Contact diagram<\/span><\/span><\/strong><\/p>\n

The wiring diagram of the overload relay is shown below,<\/span><\/span><\/span><\/p>\n

Overload relay symbol connections may look like two opposite question marks otherwise such as the “S”<\/span><\/span><\/span><\/p>\n

. The working\/function of Overload is discussed below.<\/span><\/span><\/span><\/p>\n

Although there are several types of overload relays available in the market, the most common type of relay is the \u201cbimetal thermal overload\u201d.<\/span><\/span><\/span><\/p>\n

This relay can be designed using two different types of metal strips, and these strips can be mutually connected as well as enlarged at various rates during heating.<\/span><\/span><\/span><\/p>\n

When the tape is heated to a certain temperature, the tape can twist enough to break this circuit.<\/span><\/span><\/span><\/p>\n

\"\"Overload relay diagram<\/span><\/span><\/span><\/i><\/p>\n

When the current flow towards the motor is more than what the heaters are being charged for,<\/span><\/span><\/span><\/p>\n

The overload will be detected after a few seconds. Overload categories can be classified into three types based on the duration of exploration of the sequence.<\/span><\/span><\/span><\/p>\n

Class 10, Class 20 and Class 30 overload relays can be probed after 10 seconds, 20 seconds and 30 seconds respectively.<\/span><\/span><\/span><\/p>\n

One of the main safety properties of this relay is to prevent the engine from restarting immediately.<\/span><\/span><\/span><\/p>\n

For example, when it detects an overload inside a bimetal relay, the NC (normally closed) bimetal connections will open the circuit until the strip cools down.<\/span><\/span><\/span><\/p>\n

If anyone tries to press the start switch to close the contactor switches, the engine will not start.<\/span><\/span><\/span><\/p>\n

Relay overload working<\/span><\/span><\/strong><\/p>\n

The operating principle of Overload is based on a thermoelectric property within a bimetallic strip.<\/span><\/span><\/span><\/p>\n

This can be arranged in a motor circuit such that current flows to a motor using its electrodes.<\/span><\/span><\/span><\/p>\n

When the current flow increases from the constant value, the bimetallic strip is heated and then bends.<\/span><\/span><\/span><\/p>\n

These relays always work with contactors.<\/span><\/span><\/span><\/p>\n

Once the bimetallic strips are heated, the contact trip can be energized and break the power supply towards the contactor coil, de-energized and break the current flow towards the armature.<\/span><\/span><\/span><\/p>\n

The time taken for tripping is always inversely proportional to the current flowing throughout the relay.<\/span><\/span><\/span><\/p>\n

Therefore, these relays are called current dependent relays as well as reverse time delay relays.<\/span><\/span><\/span><\/p>\n

This relay can be connected to the motor in series so that the current flow is towards the motor.<\/span><\/span><\/span><\/p>\n

When the motor is energized, the motor flowing throughout the OLR will be present.<\/span><\/span><\/span><\/p>\n

Once the excess current flows through the relay, it will trip at a certain level, therefore, the circuit between the power supply as well as the motor will be opened.<\/span><\/span><\/span><\/p>\n

After a preset period, this relay can be reset automatically or manually.<\/span><\/span><\/span><\/p>\n

Once the overload is identified and corrected, the motor will be energized again.<\/span><\/span><\/span><\/p>\n

Parts of overload relay<\/span><\/span><\/strong><\/p>\n

Apart from the contacts as well as the bimetallic strip, there are some other parts available in the overload which are discussed below.<\/span><\/span><\/span><\/p>\n

the parties<\/span><\/span><\/strong><\/p>\n

In the relay diagram, the input terminals are denoted as L1, L2 and L3 which are mounted directly towards the connector.<\/span><\/span><\/span><\/p>\n

The motor supply can be connected to terminals T1, T2 and T3.<\/span><\/span><\/span><\/p>\n

Ampere range setting<\/span><\/span><\/strong><\/p>\n

Old style rotary knob can be available.<\/span><\/span><\/span><\/p>\n

By taking advantage of this, the rated flow of current towards the motor can be adjusted.<\/span><\/span><\/span><\/p>\n

The current flow can be adjusted between the upper and lower limits provided. In electronic OLD, an additional knob is also provided to disable the separation selection<\/span><\/span><\/span><\/p>\n

Reset button<\/span><\/span><\/strong><\/p>\n

This button is available via OLD which is used to reset the relay once per trip and clear faults.<\/span><\/span><\/span><\/p>\n

Manual or automatic selection button<\/span><\/span><\/span><\/p>\n

Using these buttons, one can choose between manual and automatic reset of the relays after a trip.<\/span><\/span><\/span><\/p>\n

Once the device is repaired for automatic reset, a remote reset of the relay can be achieved<\/span><\/span><\/span><\/p>\n

Assistance point of contact<\/span><\/span><\/strong><\/p>\n

This relay includes two auxiliary contacts such as one is NO and the other is NC<\/span><\/span><\/span><\/p>\n

. For trip signals, no contact is used while for contactor disconnection, NC contact is used<\/span><\/span><\/span><\/p>\n

. NC contacts are capable of direct switching of contactor coils.<\/span><\/span><\/span><\/p>\n

Test button<\/span><\/span><\/strong><\/p>\n

The test button is used to check the control wiring.<\/span><\/span><\/span><\/p>\n

Types of overload<\/span><\/span><\/strong><\/p>\n

It is classified into two types: thermal overload and magnetic overload.<\/span><\/span><\/span><\/p>\n

Thermal overload<\/span><\/span><\/strong><\/p>\n

Thermal type relay is a protective device, which is mainly designed to cut off the power when the motor uses too much current for a long period of time.<\/span><\/span><\/span><\/p>\n

To achieve this, these relays include an NC (normally closed) relay.<\/span><\/span><\/span><\/p>\n

. Once intense current is supplied throughout the motor circuit, the relay opens due to the enhanced motor temperature<\/span><\/span><\/span><\/p>\n

, the relay temperature, and the detected overload current, based on the relay type.<\/span><\/span><\/span><\/p>\n

\"\"Thermal Overload Relay<\/span><\/i><\/p>\n

These relays are connected to circuit breakers in construction as well as application; However, most circuit breakers will disturb the circuit if an overload occurs even momentarily.<\/span><\/span><\/span><\/p>\n

These are equally designed to account for the heating profile of the engine; Thus, the overload must occur for a full period before the circuit is disconnected.<\/span><\/span><\/span><\/p>\n

Thermal overload relays are classified into two types namely solder pot as well as bimetallic strip.<\/span><\/span><\/span><\/p>\n

Magnetic overload<\/span><\/span><\/strong><\/p>\n

The magnetic overload relay can be operated by detecting the intensity of the magnetic field generated by the flow of current towards the motor.<\/span><\/span><\/span><\/p>\n

This relay can be built with a variable magnetic core inside a coil carrying the armature current.<\/span><\/span><\/span><\/p>\n

The arrangement of flux within the coil pulls the core upward. When the core gets large enough, it trips a set of contacts on top of the relay.<\/span><\/span><\/span><\/p>\n

\"\"Magnetic Overload Relay<\/span><\/i><\/p>\n

The main difference between thermal type as well as magnetic type relays is that magnetic type overload relays do not respond to the ambient temperature.<\/span><\/span><\/span><\/p>\n

Generally, these are used in areas that exhibit extreme variations within the ambient temperature.<\/span><\/span><\/span><\/p>\n

Magnetic overload relays are classified into two types namely electronic as well as drive plate.<\/span><\/span><\/span><\/p>\n

Bi-metallic thermal overload<\/span><\/span><\/strong><\/p>\n

The operation of the bimetallic thermal overload mainly depends on the heating property of the bimetal strip.<\/span><\/span><\/span><\/p>\n

In straight heating technique, the complete flow of current towards the armature can be provided using overload which is also called OLR.<\/span><\/span><\/span><\/p>\n

As a result, they are heated directly due to the flow of current.<\/span><\/span><\/span><\/p>\n

However, in the absence of direct heating, the strip can be arranged in close contact through the conductor inside the relay.<\/span><\/span><\/span><\/p>\n

The intense flow of current towards the electric motor is heated by the conductor and the bimetallic strip.<\/span><\/span><\/span><\/p>\n

Here, the conductor must be insulated, hence there will be no flow of current throughout the strip.<\/span><\/span><\/span><\/p>\n

\"\"Electronic Overload<\/span><\/span><\/strong><\/p>\n

Typically, electronic overload relays are referred to as solid-state overload relays.<\/span><\/span><\/span><\/p>\n

The interior of these types of relays does not contain a bimetallic strip.<\/span><\/span><\/span><\/p>\n

Alternatively, it includes current transducers, or temperature sensors to observe the total current flow towards the motor.<\/span><\/span><\/span><\/p>\n

For protection, this type of relay uses microprocessor-based technology. Here PTC plays a major role in detecting the temperature and also tripping the circuit once overload faults occur.<\/span><\/span><\/span><\/p>\n

Some types of overload relays come with Hall Effect sensors as well as current transformers to detect current flow directly.<\/span><\/span><\/span><\/p>\n

The main benefit of an electronic overload over a thermal overload is that it lacks the bimetallic strip which results in less heat loss in the relay.<\/span><\/span><\/span><\/p>\n

Also, these types of relays are more accurate compared to thermal relays.<\/span><\/span><\/span><\/p>\n

Some manufacturers redesign older electronics by including additional features such as ground fault protection and motor stall.<\/span><\/span><\/span><\/p>\n

Electronic overload relays are used where motors need to be turned on and off frequently.<\/span><\/span><\/span><\/p>\n

These relays can be designed in such a way that they withstand the primary current of the motor for a limited time<\/span><\/span><\/span><\/p>\n

\"\"<\/span><\/p>\n

Overload eutectic<\/span><\/span><\/strong><\/p>\n

The eutectic overload includes a coil heater, the eutectic alloy and a mechanical device to activate the tripping mechanism<\/span><\/span><\/span>.<\/span><\/span><\/span><\/p>\n

Here, the eutectic alloy is a mixture of two additional materials<\/span><\/span><\/span><\/p>\n

, which would otherwise melt, and solidify at a specific temperature. In OLR,<\/span><\/span><\/span><\/p>\n

The eutectic alloy is placed inside a tube for repeated use through a spring-loaded ratchet wheel to activate the tripping device during the overloading process.<\/span><\/span><\/span><\/p>\n

Current flows in the motor through the small heater winding during overload,<\/span><\/span><\/span><\/p>\n

The eutectic alloy tube can be heated by turning the heater and the alloy melts due to the heat so that the ratchet wheel rotates.<\/span><\/span><\/span><\/p>\n

This act begins to open the auxiliary contacts closed within the OLR. This type of relay can be manually reset once tripping is complete.<\/span><\/span><\/span><\/p>\n

Therefore, usually, this reset can be done using the reset button, which is arranged on the relay cover.<\/span><\/span><\/span><\/p>\n

The heating unit connected via the relay can be selected based on the full load current of the motor.<\/span><\/span><\/span><\/p>\n

\"Overload\"Overload for the refrigerator<\/span><\/span><\/strong><\/span><\/p>\n

A protective device such as overload is used inside the refrigerator compressor circuit.<\/span><\/span><\/span><\/p>\n

The power supply to the compressor motor windings is provided using the overloaded machine.<\/span><\/span><\/span><\/p>\n

This type of relay is mainly used to include the starter winding within the circuit so that the compressor runs at operating speed.<\/span><\/span><\/span><\/p>\n

How does the OLR guard against phase failure work?<\/span><\/span><\/strong><\/p>\n

In normal operation of OLR, the current flow through each electrode to the electric motor remains similar every time.<\/span><\/span><\/span><\/p>\n

If any phase is interrupted, the current flow through the remaining two phases increases to the usual value.<\/span><\/span><\/span><\/p>\n

So the relay and trips are heated.<\/span><\/span><\/span><\/p>\n

Phase failures are also called phase loss, otherwise single phase of the motor.<\/span><\/span><\/span><\/p>\n

These relays cannot protect against short circuit but must be used with short circuit protection devices to protect them<\/span><\/span><\/span><\/p>\n

Otherwise any short circuits inside the electric motor could easily hit it.<\/span><\/span><\/span><\/p>\n

These relays can protect against phase loss, phase imbalance, and overload, but not from short circuits.<\/span><\/span><\/span><\/p>\n

What causes OLR trip?<\/span><\/span><\/strong><\/p>\n

From the above discussion, there are three main cases of over-trip:<\/span><\/span><\/span><\/p>\n

Engine overload.<\/span><\/span><\/span><\/p>\n

Input phase loss<\/span><\/span><\/span><\/p>\n

Phase imbalance<\/span><\/span><\/span><\/p>\n

There are also some additional security features available but these vary from one designer to another<\/span><\/span><\/span><\/p>\n

Overload Trip<\/span><\/span><\/strong><\/p>\n

The time used to unlock the contactor during overloads can be indicated by the trip class.<\/span><\/span><\/span><\/p>\n

Generally, it is divided into different categories such as Class5, 10, 20 and 30.<\/span><\/span><\/span><\/p>\n

This relay trips at 5 seconds, 10 seconds, 20 seconds and 30 seconds correspondingly at full load current towards the electric motor.<\/span><\/span><\/span><\/p>\n

Commonly used overload relays are class 10 and 20 while class 30 OLR are mainly used to protect motors while operating high idle loads.<\/span><\/span><\/span><\/p>\n

Type 5 relays are mainly used for motors that require very rapid tripping.<\/span><\/span><\/span><\/p>\n

\"\"Applications<\/span><\/span><\/strong><\/span><\/h3>\n

Overload applications include the following.<\/span><\/span><\/span><\/p>\n

It is widely used for engine protection.<\/span><\/span><\/span><\/p>\n

It can be used to detect both overload conditions as well as fault conditions and then announce trip commands to the protective device.<\/span><\/span><\/span><\/p>\n

This relay has evolved into microprocessor systems as well as solid-state electronics.<\/span><\/span><\/span><\/p>\n

These relays de-energize the device when it draws excessive current.<\/span><\/span><\/span><\/p>\n

Hence, this is all about Overload overview.<\/span><\/span><\/span><\/p>\n

From the above information finally, we can conclude that these are electromechanical overload protection relays used in circuits.<\/span><\/span><\/span><\/p>\n

These devices provide consistent protection for motors during an otherwise phase failure.<\/span><\/span><\/span><\/p>\n

Here is a question for you, what is the function of Overload?<\/span><\/span><\/span><\/p>\n

What is the function of overload?<\/span><\/span><\/h2>\n

Overload is widely used to protect electric motors in particular, and it consists of two internal parts:<\/span><\/span><\/p>\n

<\/div>\n