1、 The reasonable application of relay in high voltage switch
The secondary system of high voltage switchgear currently used consists of many relays, multi contact auxiliary switches, travel switches and pressure switches, among which relay accounts for about 70%. Facing the complicated relay products, how to choose and use them correctly is a practical problem that system developers and designers pay close attention to and must be solved first, As the secondary control part of high voltage switchgear, a large number of relays are used, and they also have their unique characteristics in operation. The selection of the relays is directly related to the reliable and safe operation of substation equipment. In case of accidents, it will be particularly serious, so reasonable selection and correct application shall be made, It is necessary to fully study the practical application conditions and the requirements of the actual technical parameters of the system, and properly propose the technical performance that the relay products must achieve. In the design of the whole system, reasonable relays should be selected according to the importance, reliability, environmental conditions and cost of the whole system.
The main factors of climate stress are temperature, humidity, atmospheric pressure (altitude), coastal atmosphere (salt fog corrosion), dust pollution, chemical gas and electromagnetic interference, etc. Considering that the high-voltage switch operates under many severe working conditions, especially when it is used as an open type high voltage circuit breaker equipment in outdoor environment, the working condition is worse, And the special of reliable operation over the years and the key parts of the system must be full sealed products with high altitude and strong electrical resistance. Only fully sealed relays can have excellent long-term ability of withstanding harsh environment, good electrical contact stability and reliable switching load.
1. the influence of temperature on relay
Relay is a thermal element, high temperature can accelerate the aging of internal plastic and insulation materials of relay, contact is oxidized and corroded and arc extinguishing is difficult. Technical parameters of electrical components decay and reliability is reduced. Because the high-voltage switch is equipped with a moisture driven and heat preservation heater, it is not allowed to close the relay to the heater of moisture and heat preservation during the design of the whole system, And good ventilation conditions should be maintained. Although the relay is a thermal element, the low temperature can not be ignored. Low temperature can aggravate the cold adhesion of the contact and expose the contact surface. Many manufacturers' relays indicate that the minimum temperature is one and 25 ℃, but the high voltage switch is not used in the cold area. Therefore, there is room for selection of the relay to avoid the unreliability of the relay due to low temperature, Add heater in the cold area to ensure reliable operation of relay at low temperature and ensure the stability of the whole system.
2. effect of low air pressure on relay
Under low air pressure, the heat dissipation condition of relay becomes bad, and the coil temperature increases, which changes the parameters of relay's suction and release, which affects the normal operation of relay. Low air pressure can also reduce the insulation resistance of relay, and it is difficult to extinguish arc of contact, which makes contact burn-up easily, and affects the reliability of relay. In view of low air pressure conditions, the relay can be used to reduce the insulation resistance of relay, It is suggested to adopt the method of sealing the whole machine.
3. the influence of mechanical stress on relay
It mainly refers to the anti earthquake stress and mechanical stress effect of vibration, impact and collision on the control system. The vibration caused by the self vibration and opening and closing operation of the breaker in high voltage on / off has greater influence on the relay. The middle relay of balanced armature mechanism should be selected. For the reed of electromagnetic relay, it is of suspension beam structure with low natural frequency, Vibration and shock can cause resonance, which leads to the pressure drop of relay contacts, which is easy to break or shake the contact, which affects the reliability of relay. It is suggested that vibration prevention measures should be taken as far as possible in the design to prevent resonance.
4. influence of insulation voltage on relay
The exposed insulator at the outlet of the non sealed or sealed relay is polluted by dust and water for a long time, which leads to the decrease of insulation strength and the failure of insulation breakdown.
It mainly refers to the contact load properties, such as lamp load, motor load, inductor, contactor (relay) coil, resistance load, etc; Contact load value (open circuit voltage value, closed-circuit current value), such as low level load, dry circuit load, small current load, large current load, etc.
Any automation equipment must be determined the actual load nature and the load value. It is very important to select the appropriate relay products. The failure or reliability of relay mainly refers to whether the contact can complete the specified switching circuit function. If the actual load of switching is inconsistent with the switching load specified by the selected relay, the reliability will be impossible to talk about.
Special problems and analysis of relay in use
1. about sealing relay and non sealing relay
Some engineering technicians think that the non sealing products act intuitively and the failure analysis is convenient. However, the whole sealing product can not be seen through the action process. The subjective recognition of non sealing products is more reliable than the whole sealed products. This intuitive concept is very wrong.
The advantages of non sealing relay are that the clapping armature is used, which has simple structure, simple manufacturing process, convenient installation and maintenance, intuitive working status, easy failure analysis and low price. The main disadvantage is that the working reliability is sensitive to the change of the environment (climate stress and mechanical stress). The long-term performance of the weather conditions is easy to be polluted and damaged by the environmental conditions with time. The stability and reliability of electrical contact are poor. The coil is prone to moisture and impurities pollution, resulting in electrical corrosion and mildew failure.
The advantages of the full seal relay are that balanced rotating armature is used. The whole sealing mechanism isolates the external climate stress, and has excellent performance against adverse environment, stable and reliable contact performance of contacts, corrosion resistance and mildew resistance of coil, excellent long-term reliability performance, and the disadvantage is complex structure, complex manufacturing process, difficult failure analysis, and can not be reused after maintenance, and high cost and price.
Therefore, considering the reliability of long-term weather stress resistance, anti-harsh environment performance and electrical contact stability, the full seal relay is better than non sealed relay, especially for the products using relay in high voltage switch, full sealing relay should be selected, so it can meet the special requirements of automatic control of electric force and long-term stability.
2. parallel and series connection of relay contacts
The use of relay contacts in parallel can not improve the load current, because the action of multiple groups of contacts of relay is absolutely different. That is, the first group of contacts connected first switches the load after the increase, while the other contacts in parallel have not yet acted, so it is easy to damage the contacts without contact or welding, and the failure rate can be reduced by the parallel connection of contacts, But for "sticking" fault, because contact to "break" fault is the main failure mode, parallel connection should be sure to improve reliability, and can be used in key parts. For example, when the high voltage circuit breaker realizes three pole electrical linkage, three pairs of normally open contacts are closed by relay action, and three single pole electromagnets are respectively driven to complete the opening and closing operation. At this time, the relay, namely, 3 pairs of normally open contacts of the opening and closing relay can be connected in two groups, which plays a key role, as shown in Figure 1. The working voltage used shall not be higher than the maximum working voltage of relay coil and 90% of rated voltage, otherwise, the life and reliability of the coil will be endangered.
The series connection of contacts can improve the load voltage, and the multiple of the increase is the number of series contacts. The reliability of the contact series pair "sticking" fault can be improved, but the opposite is for the "break" fault.
For example, in some high voltage circuit breakers, the contact of auxiliary switch is connected in parallel or in series in the open and closing operation circuit, which is determined by the operating load current. In order to operate more reliably, it is recommended to parallel the auxiliary switch contacts to ensure reliable operation and play a key protection role. As shown in Figure 3.2, it is recommended to use figure 3 parallel type.
|<12>>
2、 Correct connection of relay contacts
(1) In the operation of power automation control, the dynamic contact shall be used as much as possible, and the dynamic contact shall be used as much as possible. In other words, when the relay contacts are connected, the dynamic contact connection mode shall be adopted as much as possible. The dynamic contact shall be less used, because the relay of the dynamic contact shall have less contact bounce times than the relay of the dynamic contact when it is operated, and the contact jitter can cause adverse effect on the circuit, Shorten the life of the contacts.
(2) The positive and negative polarity of relay contacts shall be reliably connected. For relay with positive and negative polarity connection, the positive pole must be connected to the positive Q1 ~ auxiliary switch SB1 one close control button K1 electromagnet power supply, and the negative pole must be connected to the negative power supply, indicating the positive and negative polarity, otherwise, the next stage design may be connected incorrectly, causing the relay to not act or fail.
Selection of relay
In three-phase AC motor, the motor is burnt out due to the fault of line and phase missing operation of motor. In order to solve this kind of accident, most designers choose thermal relay with phase missing protection, but the reasonable selection of thermal relay must be selected according to the following requirements:
(1) For the motor running stably for a long time, take 0.9-1.05 times of the set current of the thermal relay or the intermediate value equal to the rated current of the motor. When using, adjust the setting current of the thermal relay to the rated current value of the motor;
(2) Generally, the rated current of thermal relay shall be greater than the rated current of motor, and then the model of thermal relay shall be selected according to the rated current. When the starting current of motor is 6 times of its rated current or the starting time is more than 5S, the setting current of thermal element shall be adjusted to the rated current of motor; When the motor starts for a long time, drives the impact load or does not allow to stop, the set current of the thermal element is adjusted to 1.1-1.5 times of the rated current of the motor;
(3) If the thermal relay is tripped due to line failure or other reasons, reset means shall be adopted. Generally, the thermal relay is set with two specifications: self reset and manual reset. It is recommended to set to manual reset in normal use to ensure that the thermal relay can be reset after the fault is processed.
Relay coil in parallel
In the complex control circuit, two (or more) different types of relays (such as contactor K1 and small sensitive relay K2) coils are used in parallel by the method shown in Fig. 4. In this case, K1 may be generated, delay release, contact arc breaking capacity is decreased, K2 is repeatedly stimulated in reverse, contact misoperation and other practical problems may occur. Because in DC control circuit, the magnetic energy stored by K1 and K2 coils may vary greatly. When switch q is off, the energy storage of K1 (large magnetic energy) will be discharged through the coil K2 (small magnetic energy), and the reverse current will be generated. Thus, the K1 release time is prolonged, the contact arc breaking speed is slow, and the arc burning time between contacts is prolonged; The release time of K2 is short, and then it is excited by reverse discharge current, and even repeatedly absorbed after release, resulting in misoperation fault.
In order to eliminate the influence of the above factors, it is recommended to use the control circuit shown in Figure 5. This is because after series connection of each auxiliary normally closed contact on each relay circuit, K1 and K2 lose power after switch q is disconnected, auxiliary normally closed contact on their respective circuits becomes open contact, so that K1, K2 and other relays will not affect each other and cause misoperation.
On the use of relay coil series
Many users of power system use multiple relay coils in series and then use dc220v power supply to stimulate (as shown in Figure 6). This excitation method shall not be used as far as possible.
(1) For the same type and the same specification relay products, because the impedance of each coil (including DC resistance and instantaneous inductance) is basically the same and the difference is small, the problem of using series voltage sharing excitation is not very small, and the practice proves to be feasible.
(2) For different types or specifications of relays, because the impedance of different relay coils is inconsistent and the difference is very different with the instantaneous reactance, the difference between the excitation voltage (determined by the instantaneous voltage sharing ratio) on the coil of each relay must be very large at the moment of series excitation, and some relays will be in the over voltage excitation state, Some are under voltage excitation. The switch timing and speed of each relay contact will change substantially. It is inevitable that the action is first, then, fast and slow reverse, and the switch is unreliable. Therefore, the series voltage splitting excitation method is not suitable for different types and different specifications of relay coils.