What does it mean when a motor is thermally protected? When you see the term "thermal protection" or "thermally protected" used in the description of an electric motor, it refers to a device found within the motor or motor compressor that is designed to prevent dangerous overheating that can cause motor failure. Click to see full answer.
What is thermal protection on a motor?
08/04/2020 · Thermal protection is a method of fan motor protection that is activated when a motor operating at the rated voltage locks up for some reason with the power still being supplied. It uses a thermal relay inside the motor to break the circuit to the winding coil at a temperature below the level that would cause burning.
Which type of protection has been applied to a motor?
10/01/2021 · Thermal protection is a method of fan motor protection that is activated when a motor operating at the rated voltage locks up for some reason with the power still being supplied. It uses a thermal relay inside the motor to break the circuit to the winding coil at a temperature below the level that would cause burning.
What is the difference between built-in motor protection and thermal overload protection?
Thermal protection is a method of fan motor protection that is activated when a motor operating at the rated voltage locks up for some reason with the power still being supplied. It uses a thermal relay inside the motor to break the circuit to the winding coil at a temperature below the level that would cause burning.
What does “thermally protected” mean?
11/03/2021 · The thermistors are built into the motor windings and protect the motor against locked-rotor conditions, continuous overload and high ambient temperature. Thermal protection is then achieved by monitoring the temperature of the motor windings with PTC sensors.
What does a thermally protected motor mean?
Thermal protection is a method of fan motor protection that is activated when a motor operating at the rated voltage locks up for some reason with the power still being supplied. It uses a thermal relay inside the motor to break the circuit to the winding coil at a temperature below the level that would cause burning.
What is thermal overload protection in motor?
Thermal overload relays are economic electromechanical protection devices for the main circuit. They offer reliable protection for motors in the event of overload or phase failure. The thermal overload relay can make up a compact starting solution together with contactors.
What's thermal protection?
Thermal protection is a method of detecting over-temperature conditions and disconnecting the power to the electronic circuits. The protection prevents fires or damage to electronics components, which may arise due to the excess heat in the power supplies or other equipment.
Why must the motor needs thermal overload installed?
In order to avoid unexpected breakdowns, costly repairs and subsequent losses due to motor downtime, it is important that the motor is fitted with some sort of protective device. This article will deal with built-in motor protection with thermal overload protection to avoid damage and breakdown of motor.15-May-2015
How does thermal overload protection work?
The thermal overload relay is designed to protect the motor or other load from damage in the event of a short circuit, or being over-loaded and overheating. The simplest overload relay is activated by heat caused from high current flowing through the overload and over a bimetallic strip.24-Aug-2017
What determines the thermal loading on motor?
The thermal loading on the motor is determined by the duty/load cycle. One important consideration with totally enclosed fan cooled (TEFC) motors is that the cooling may be insufficient when the motor is operated at speeds lower than its rated speed.
What happens if you don't use heat spray?
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How do I know if my heat protectant is working?
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Do you put heat protectant before or after?
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How is thermal overload protection done in motors using contactors?
In a bimetallic thermal overload relay, heating due to current flow causes the bimetallic strip to bend to one side, activating a trip mechanism. ... When the strip bends, it actuates a normally closed (NC) contactor, causing it to open and stopping the current flow to the motor.21-Oct-2020
What causes a thermal overload to trip?
A common reaction to an overloaded motor that repeatedly trips its protection unit (or burns open its “heaters”) is to “upgrade” the protection. ... Causes may include a large change in load (e.g., a scrap grinder is fed too much at a time), misalignment, a broken drive gear, or improper motor drive settings.25-Jan-2016
How can a motor be protected from overheating due to sustained motor overload?
Overload relays (thermal or electronic) protect motors against overloads, but they must allow the temporary overload caused by starting, and must not trip unless the starting time is abnormally long.12-Jan-2020
Why is it important to have a motor fitted with thermal overload protection?
In order to avoid unexpected breakdowns, costly repairs and subsequent losses due to motor downtime , it is important that the motor is fitted with some sort of protective device. This article will deal with built-in motor protection with thermal overload protection to avoid damage and breakdown of motor.
What is the IEC 60034-11?
The degree of protection that an internal protection device provides is classified in the IEC 60034-11 standard.
Can a thermal switch be used without a heater?
Thermal switch with heater. Thermal switch without heater for three-phase motors (star-point protector) A thermostat can either energize an alarm circuit, if normally open, or de-energize the motor contactor , if normally closed and in series with the contacto r.
What is thermal protector?
Thermal protectors are also referred to as Klixons, (trade name from Texas Instruments). When the bi-metal disc reaches a predetermined temperature, it opens or closes a set of contacts in an energized control circuit.
Can thermal switches be retrofitted?
Thermal switches can be retrofitted on the coil end, but the result is an increased reaction time. The switches have to be connected to an external monitoring system. In that way the motor is protected against a slow overload. The thermal switches do not require an amplifier relay.
What is the second type of internal protection?
Thermistors – also built into the windings. The second type of internal protection is the thermistors or Positive Temperature Coefficient sensors (PTC). The thermistors are built into the motor windings and protect the motor against locked-rotor conditions, continuous overload and high ambient temperature.
What is PTC protection?
PTC protection built into windings. Only temperature sensitive. The thermistor has to be connected to a control circuit, which can convert the resistance signal, which again has to disconnect the motor. Used in three-phase motors.
Why does my motor overheat?
Another cause of overheating is low supply voltage. As the power id drawn by the motor from the supply depends upon the loading condition of the motor, for lower supply voltage, motor will draw higher current from mains to maintain required torque. Single phasing also causes thermal over loading of motor.
What happens when the magnetic flux cuts each bar conductor of a rotor?
As the rotating magnetic flux cuts each of the bar conductor of rotor, there will be an induced circulating current flowing through the bar conductors. At starting the rotor is stand still and stator field is rotating at synchronous speed, the relative motion between rotating field and rotor is maximum.
How long can a motor run at 100 % load?
Here it is clear from the curve that, motor can run safely without any damage due to overheating for prolonged period at 100% of the rated load. It can run safely 1000 seconds at 200 % of normal rated load. It can run safely 100 seconds at 300 % of normal rated load.
Can a rotor stop running?
Due to this phenomenon the rotor will never achieve the synchronous speed as well as it will never stop running during normal operation. The difference between the synchronous speed with rotor speed in respect of synchronous speed, is termed as slip of induction motor.
Why does an unbalanced motor winding cause over heating?
Again, due to sudden loss and reestablish of supply voltage may cause excessive heating of the motor.
What causes thermal over loading of motor?
Single phasing also causes thermal over loading of motor. When one phase of the supply is out of service, the remaining two phases draw higher current to maintain required load torque and this leads to overheating of the motor.
What are the disadvantages of bimetallic thermal relays?
There is one main disadvantage of bimetallic thermal over load relay, as the rate of heating and cooling of bi-metal is affected by ambient temperature, the performance of the relay may differ for different ambient temperatures. This problem can be overcome by using RTD or resistance temperature detector.
Why do motors need to be housed in enclosures?
Special cases. Some applications require that a motor be housed in an enclosure for noise abatement or other reasons. In such cases, special care should be taken to control the ambient temperature inside the enclosure where the motor is located.
What is ambient temperature?
Second, ambient temperature refers to the temperature of surrounding air. Some people confuse this with the expected temperature rise of the motor, which it is not.
Do motors have to run at the maximum temperature?
Thermal protection and the correspondingly higher temperature limits are generally reserved for smaller motors. Even then, however, motor manufacturers will not design a motor to run at the maximum temperature allowed unless application considerations make it necessary.
Why is temperature control important?
Temperature control is an important factor in successful motor operation. Care must be taken in the design, application and maintenance of these machines to optimize their performance and life. Having said all that, it is unsafe to place your hand on a motor to see if it is too hot; get a thermometer instead.
Is auxiliary cooling adequate?
Cooling is usually adequate if the auxiliary cooling supplies the same volume of air as the motor’s integral fan. If the driven equipment generates heat (e.g., a compressor) and is contained in the motor enclosure, it can contribute to the temperature rise of the motor.
What is the voltage rating of a three phase motor?
NEMA defines standard voltage rating for three-phase motors. Some common ratings are 200, 230, 460, and 575 volts. NEMA allows motors to operate at plus or minus 10% of the nameplate voltage rating, while pointing out that this may degrade performance or efficiency.
What is the service factor for a motor?
The service factor is only required ion a nameplate if it is higher than 1.0. Industry standard service factors include 1.0 for totally enclosed motors and 1.15 for open motors. Totally enclosed fan cooled motors with a 1.15 service factor are also widely available, and values of 1.25, 1.4 and higher exist.
Overview
Causes
- This overheating generally occurs when the motor is overloaded, when a bearing seizes up, when something locks the motor shaft and prevents it from turning, or when the motor simply fails to start properly. A failure to start may be caused by faulty start windings in the motor.
Mechanism
- The thermal protector consists of one or more heat-sensing elements built into the motor or motor-compressor, plus an external control device. The thermal protection is present to turn the motor off when excessive heat is generated within the motor circuitry, halting the temperature climb before it can burn up the motor.
Operation
- These thermal protectors reset themselves once the motor cools down to a safe operating temperature. There is usually a visible red button located on the wiring side of the motor usually, though not always, located opposite of the motor shaft. On motors equipped this way, you must press the reset button to reset and restart the motor. On other motors without a reset button, th…
Example
- A sump pump is a motor for which this scenario often occurs. If a sump pump pumps water filled with debris, pieces of debris may get caught in the impeller and lock the rotation of the pump motor, causing it to overheat very quickly. On a pump equipped with thermal protection, the device will trip and shut down the circuit to the motor windings. This will allow the motor to cool down …
Variations
- The same scenario may be true on other electric motors that process variable loads, such as garbage disposers, washing machines or vacuum cleaners. Without thermal protection, such motors can be more prone to burn-out.
Advantages
- \"Thermal protection\" is generally a good feature to look for when buying equipment with electrical motors. By protecting the motor from overheating, it can greatly extend the life of the motor.