What is the Setting Method of the Over Current Relay? Principle of Over Current Relay

Over current relays are divided into induction electromagnetic type and integrated circuit type, which have the characteristics of definite time limit and inverse time limit, and are used in main equipment such as motors, transformers, and over current relay protection circuits of power transmission and distribution systems. When the main equipment or power transmission and distribution system is overloaded or short-circuited, the over current relay can reliably act or send a signal according to the predetermined time limit, and remove the faulty part to ensure the safety of the main equipment and power transmission and distribution system.

1. Introduction of over current relay

The action principle of the over current relay is a compound type, which consists of two components of inductive type and electromagnetic type, and the two components share a coil. When the coil is supplied with alternating current, in the electromagnet of the induction element, due to the phase shifting effect of the short-circuit ring, two magnetic fluxes with different phases are generated, and the magnetic flux interacts with the eddy current induced in the aluminum disk to generate electromagnetic force Make the aluminum disk rotate, when the current increases to the set current, the electromagnetic torque is greater than the reaction torque of the spring, the aluminum bracket rotates, the fan teeth and the worm are engaged, and rise with the rotation of the worm, and the ejector rod pushes the moving iron of the electromagnetic element , when the air gap between the moving iron and the electromagnet is reduced to a certain extent, the moving iron is attracted, the top plate at the end of the moving iron pushes the contacts to close, and pushes down the signal plate to display the over current relay over-current state.

2. Equipment introduction of over current relay

2.1 Principle
The working principle of the electromagnetic over current relay is a composite type, which consists of two components, the induction type and the electromagnetic type, which share a coil. When the coil of the over current relay is supplied with alternating current, two magnetic fluxes with a certain phase difference are generated in the shielded and unshielded parts of the iron core. This magnetic flux interacts with the eddy currents it induces in the disc, producing a torque on the disc. Under the operating current setting value of 20% to 40%, the disk starts to rotate. At this time, because the fan teeth do not engage with the worm, the over current relay does not act.

When the current in the coil increases to the set current, the electromagnetic torque is greater than the reaction torque of the spring, and the frame rotates, so that the fan teeth and the worm are engaged, and the fan teeth rise. At this time, the moving iron of the over current relay is pushed by the fan tooth ejector rod to reduce the air gap on the right side of the guide magnet and increase the air gap on the left side, so the moving iron is attracted by the guide magnet to make the over current relay contact act.

When the current in the over current relay coil is the set value, the action time limit of the inductive element is inversely proportional to the square of the current. As the current increases, the magnetizer is saturated, and the action time gradually tends to a constant value. When the current in the coil is greater than a certain current multiple, the electromagnetic element acts instantaneously, so the action time limit of the over current relay has the characteristic of limited anti-delay.

The over current relay has several taps, which are used to adjust the operating current of the induction element and the electromagnetic element. In addition, use the current doubler screw to change the air gap between the moving iron and the electromagnet to adjust the operating current of the electromagnetic element. The over current relay has a mechanism for adjusting the setting value of the action time of the sensing element and a signal plate for the action of the main contact. Rotate the return mechanism by hand to return the signal plate without removing the housing.

2.2 Technical parameters
2.2.1 The rated current and setting range of the over current relay.
2.2.2 The long-term allowable current of the over current relay coil is 110% of the rated current.
2.2.3 The return coefficient of the over current relay should not be less than 0.85 for GL-11, 12, 21, 22 types, and not less than 0.8 for GL-13, 14, 15, 16, 17, 23, 24, 25, 26 types.
2.2.4 When the current is the set current of the over current relay, the power consumption of the over current relay shall not exceed 15VA.

2.3 Rated working voltage
The rated working voltage refers to the voltage required by the coil when the over current relay works normally. Depending on the type of over current relay, it can be AC voltage or DC voltage.

2.4 DC resistance
DC resistance refers to the DC resistance of the coil in the over current relay, which can be measured by a multimeter.

2.5 Pickup current
The pick-up current refers to the minimum current that the over current relay can produce a pick-up action. In normal use, the given current must be slightly greater than the pull-in current, so that the over current relay can work stably. As for the working voltage applied to the coil, generally do not exceed 1.5 times the rated working voltage, otherwise a large current will be generated and the coil will be burned.

2.6 Release current
The release current refers to the maximum current for the over current relay to produce a release action. When the current in the pull-in state of the over current relay decreases to a certain extent, the over current relay will return to the release state without power. At this time, the current is much smaller than the pull-in current.

2.7 Voltage and current
Contact switching voltage and current refers to the voltage and current that the over current relay is allowed to load. It determines the size of the voltage and current that the over current relay can control, and it cannot exceed this value when used, otherwise it is easy to damage the contacts of the over current relay.

2.8 Contact performance

a. Moving main contact performance
When the voltage of the moving main contact is not greater than 250V, it can connect DC or AC 5A, but to disconnect the circuit it connects, it should be served by other contacts (such as the auxiliary contact of the oil switch).

b. Breaking main contact performance
DC inductive (τ=5ms) circuit, U≤250V, I≤0.5A, 50W; AC (cosФ=0.4) circuit: U≤250V, I≤2A, 250VA.
If the controlled circuit is powered by a converter and connected in parallel with the main contact of the over current relay, and when the current is 4A, its total impedance is not greater than 4Ω, then the main contact of the over current relay can shunt this circuit when the current is not greater than 50A On and off.

c. Transition switching main contact performance
The main contact control circuit of the transition conversion of the over current relay is powered by the converter, and its impedance value is not greater than 4.5Ω when the current is 3.5A. When the current increases to 150A, the main contact of the over current relay can shunt and shunt the circuit disconnect.

d. Signal Contact Performance
The moving and closing signal contact of the over current relay can connect or disconnect a DC non-inductive circuit with a current of not more than 0.2A or an AC circuit with a current of not more than 0.5A when the voltage is not greater than 250V.

2.9 Thermal Performance Requirements
When the ambient temperature is 40°C, the over current relay coil withstands 110% of the rated current for a long time, and its maximum allowable temperature rise does not exceed 65°C.

2.10 Dielectric Strength
Insulation resistance is not less than 300MΩ, all circuits of the over current relay should be able to withstand 2kV (effective value) 50Hz AC test voltage for 1min, without insulation breakdown or flashover phenomenon.

2.11 Lifespan
GL-11～14, 21～24 type over current relays have a mechanical life of 5000 times and an electrical life of 500 times;
GL-15, 16, 17, 25, 26 over current relays have a mechanical life of 500 times and an electrical life of 500 times.

3. Over current relay

3.1 Purpose
JGL- 10 series static inverse time over current relays have inverse time characteristics and are used in relay protection devices for generators, transformers and power transmission and distribution systems. When the equipment is overloaded or short-circuited, it can reliably act according to the predetermined time limit, send out a signal or remove the faulty part.
This over current relay is an integrated circuit static relay. It uses a digital switch to set the current value, which is intuitive and convenient. It does not need to be inspected when changing the setting value. The setting range is 2-9.9A with a step difference of 0.1A. High, it is an ideal replacement product for GL-type over current relay.

3.2 Normal environment
3.2.1 Ambient temperature: -10℃～+50℃;
3.2.2 Relative humidity: not more than 90%;
3.2.3 Atmospheric pressure: 86kPa～106kPa;
3.2.4 There shall be no vibration exceeding the severe level 1 specified in GB/T14537 at the place of use.
3.2.5 Surrounding environment: direct sunlight, rain and water washing are not allowed, and there is no explosion hazard medium. It should not contain medium and conductive medium that can corrode metal, damage insulation and surface coating, and no obvious water is allowed. Gas, serious mold is not allowed to exist.

3.3 Technical indicators
3.3.1 Rated value: AC 5A at 50Hz, waveform distortion does not exceed 2%.
3.3.2 The overcurrent setting range is 2-9.9A (without auxiliary power supply), the step difference is 0.1A, and the error of the current setting value is not more than ±3%.
3.3.3 The setting range of quick action multiple is 2-9.9 times, the step difference is 0.1 times, and the error of current quick action setting value is not more than ±3%. The quick current of the over current relay is expressed by the multiple of the current setting value: quick current = quick multiple × setting current.
3.3.4 Snap action time: at any setting point of the over current relay, the action time at 1.2 times the snap current is not more than 50ms.
3.3.5 Return coefficient: not less than 0.9.
3.3.6 Action equation of inverse time characteristic curve: t: inverse time action time K: delay curve coefficient (setting range 0.1～9.9). Is: Setting current value I: Actual input current value (Note: I/Is not greater than 1.2 is not recommended for use).
3.3.7 Inverse time characteristic time setting error:
a) When I/Is<2, the average error is not greater than 10%;
b) When I/Is>2, the average error is not greater than 5%+30ms.

4. Setting method

4.1 Starting current setting: The starting current setting switch is the leftmost group of DIP switches (two in total), the left one indicates 1A level, and the right one indicates 0.1A level. If its value is 5 and 6, its setting value is 5.6A. Note that its range is 2-9.9A for products without auxiliary voltage, and the level difference is 0.1A.

4.2 K value setting of inverse time characteristic curve: The K value setting switch is the third group of DIP switches on the left (two in total), the one on the left indicates level 1; the one on the right indicates level 0.1. The K value setting range of this product is 0.1~9.9, (for example) if its value is set to 5.0, the over-current action value is set to 5.0, when the actual input current is 30A, then its delay time is 13.5 seconds, but its quick break The multiplier value should be set to 6 times or more.

4.3 Snap multiplier setting: The snap multiplier selection switch is the second group of dial switches on the left, and its range is 2-9.9 times. The left one of the dial means 1 times, and the right one means 0.1 times. When its value is 3 or 0, it is 3 times. If the set current is 2.6A and the quick action multiple is 3 times, then when the current reaches 3×2.6=7.8, it will act directly without delay. Note that the product without auxiliary power supply can only be returned after a power failure.