1. Primary loop/primary loop and primary device/primary device
Refers to the power transmission and distribution circuit, its main task is to carry out the transmission and distribution of electric energy. The equipment connected to it is called primary equipment or main equipment, such as transformers, circuit breakers, fuses, ground knife switches, transmission and transformer distribution cables, etc. Usually the terminal electrical equipment, such as: motor (motor), lighting, etc., is also included in the scope of primary equipment. It can also be understood that the primary circuit is composed of transmission and distribution cables + main equipment (transformers, circuit breakers, etc.) + electrical equipment (motors, lights, etc.).
2. Secondary loop/control loop and secondary equipment/control equipment
Refers to the primary equipment for control, indication, measurement (measurement), monitoring and protection of the loop, its main task is to monitor the operating status of the primary loop, operating parameters, etc., to ensure the normal operation of the loop. The equipment connected to it is called secondary equipment or control equipment, also known as control appliances, including: PT (voltage transformer), CT (current transformer), contactors, relays, integrated protection devices, circuit breaker auxiliary contacts, various operating buttons, metering instruments, control cables of secondary circuits, etc.
3. Switch cabinet
It refers to a complete set of power distribution device assembled by primary equipment and secondary equipment according to a certain line plan, which is used to control and protect the line and equipment, divided into fixed and hand-operated, and can be divided into high-voltage switchgear (fixed and hand-operated) and low-voltage switchgear (fixed and drawer type) according to the voltage level of the incoming and outgoing line. The structure of the switchgear is generally similar, mainly divided into bus room, circuit breaker room, secondary control room (instrument room), feeder room, and there is generally steel plate isolation between the rooms.
Internal components include: bus (bus bar), circuit breaker, conventional relay, integrated relay protection device, metering instrument, isolation knife, indicator light, grounding knife, etc.
From the perspective of application:
Incoming cabinet: also known as the receiving cabinet, is used to receive electrical energy from the power grid equipment (from the incoming line to the bus), generally installed with circuit breakers, CT, PT, isolation knife and other components.
Outlet cabinet: also called feed cabinet or distribution cabinet, is used to distribute electrical energy equipment (from the bus to each outlet), generally installed with circuit breakers, CT, PT, isolation knife and other components.
Busbar liaison cabinet: also called busbar breaking cabinet, is used to connect two busbar equipment (from the busbar to the busbar), in the single busbar segment, double busbar system is often used to connect the busbar, in order to meet the requirements of users to choose different operation modes or to ensure that there is a choice of cutting load in the case of failure.
PT cabinet: Voltage transformer cabinet, generally installed directly on the bus to detect the bus voltage and achieve protection function. Inside the main installation of voltage transformer PT, isolation knife, fuse and lightning arrester.
Isolation cabinet: It is used to isolate the bus at both ends or to isolate the power receiving equipment and the power supply equipment, and it can provide the operator with a visible endpoint to facilitate maintenance and overhaul operations. Since the isolation cabinet does not have the ability to break and switch on the load current, the handcart of the isolation cabinet cannot be pushed and pulled when the circuit breaker matched with it is closed. In general applications, it is necessary to set the circuit breaker auxiliary contact and the isolation of the interlock, to prevent the operator's misoperation.
Capacitor cabinet: also called compensation cabinet, is used to improve the power factor of the power grid, or for reactive power compensation, the main device is a group of capacitor banks in parallel, switching control circuit and fuse and other protective appliances. It is generally installed side-by-side with the incoming cabinet, and one or more capacitor cabinets can be run side-by-side. After the capacitor cabinet is disconnected from the power grid, because the capacitor bank takes a period of time to complete the discharge process, it is not possible to touch the components in the cabinet directly by hand, especially the capacitor bank; Within a certain period of time after power failure (depending on the capacity of the capacitor bank, such as 1 minute), it is not allowed to re-close, so as to avoid overvoltage damage to the capacitor. When performing the automatic control function, it is also necessary to pay attention to the reasonable allocation of the switching times of each group of capacitor banks, so as to avoid the situation that one group of capacitors is damaged while the other groups are rarely switched.
Measuring cabinet: mainly used for measuring electricity (KWH), and high voltage, low voltage points, generally installed with isolating switches, fuses, CT, PT, active power meters (traditional meters or digital meters), reactive power meters, relays, and some other auxiliary secondary equipment (such as load monitoring meters, etc.).
GIS Cabinet: Also known as Gas-Insulated metal-enclosed Switchgear, it is a circuit breaker, isolation switch, ground switch, CT, PT, lightning arrester, bus and other closed combination in a Metal shell. Then, gas with good insulation performance and arc extinguishing performance (generally sulfur hexafluoride SF6) is used as an interphase and ground insulation measure, which is suitable for high-voltage and high-capacity power grids for distribution and control.
4. Circuit breaker
Under normal operating conditions, the circuit breaker is in the closing state (except for special applications), and the circuit is switched on. When the automatic control or protection control operation is carried out, the circuit breaker can be broken or switched on under the control of the comprehensive protection device. The circuit breaker can not only break the normal load current, but also can withstand a certain period of short circuit current (several times or even dozens of times the normal working current), and can break the short circuit current, cut off the fault line and equipment. Therefore, the main function of the circuit breaker is to break and connect the circuit (including breaking and connecting the normal current, breaking the short circuit current).
Because in the process of breaking and connecting the circuit, the arc is inevitably generated between the moving contact and the static contact of the circuit breaker. In order to protect the contacts, reduce the loss of the contact material and reliably break the circuit, measures must be taken to extinguish the arc as soon as possible, one of which is to fill the dynamic and static contacts of the circuit breaker with different arc extinguishing media. According to the different circuit breakers of the arc extinguishing medium can be divided into: oil circuit breaker (more oil, less oil), sulfur hexafluoride (SF6) circuit breaker, vacuum circuit breaker, air circuit breaker, etc. The main primary equipment in the high and low voltage switchgear that we often come into contact with in the project is the circuit breaker.
Since the dynamic and static contacts of the circuit breaker are generally wrapped in a container full of arc extinguishing media, the split and close state of the circuit breaker can not be directly judged, generally through the auxiliary devices of the circuit breaker (such as the split and close pointer, etc.) to determine.
5. Spacer knife
Isolation knife (or isolation switch) because there are obvious breaks can be identified on or off, mainly used to isolate high-voltage power supply, to ensure the safety of the line and equipment maintenance, can break the current is very small (generally only a few amps). Since there is no special arc extinguishing device, it cannot be used to break fault current and normal working current, and it is not allowed to break operation with load.
6. fuse
The fuse is a simple circuit protection appliance, the principle is that when the current flowing through the fuse reaches or exceeds a certain value after a certain time, the melt itself melts and cuts off the circuit. Its operation principle is simple, easy to install, generally not used alone, mainly used to cooperate with other electrical appliances.
Main action features:
First, the current should reach a certain value, which has been done before the fuse factory and cannot be changed;
Second, the current reaches a certain value after a certain time, the time is also done by the manufacturer, can not be changed, but there are many types, including delay action, fast action, super fast action, etc.;
Third, the body is damaged after the action, can not be reused, must be replaced;
Whether the fuse is blown can be judged by the fuse indicator or by the appearance of the melt. Commonly used fuses and safety tubes belong to this kind of electrical appliance.
Seven. Load switch
The load switch has a simple arc extinguishing device, and the arc extinguishing medium generally uses air, which can connect and break a certain current and overcurrent, but can not break the short circuit current, and can not be used to cut off the short circuit fault. Therefore, it is absolutely not allowed to replace the circuit breaker with a load switch; If the load switch is to be used, it must be used in conjunction with the high-voltage fuse mentioned earlier (in fact, the fuse and the load switch are often used in series for simple overload protection to reduce the engineering cost).
The load switch is similar to the isolation knife, which has an obvious disconnect gap and can easily determine whether the circuit is on or off.
8. transformer
Simply put, a transformer is a device that uses alternating electromagnetic fields to convert different voltage levels (in fact, the conversion of electrical energy), and the voltage before and after the transformation does not change in frequency. According to its use can be divided into many kinds, such as power transformer, rectifier transformer, voltage regulator, isolation transformer, as well as CT, PT and so on. What we often encounter in engineering sites is power transformers.
Some of the main technical parameters related to transformers include:
Rated capacity: refers to the rated output capacity of the transformer under rated working conditions (equal to U×I, unit is kVA);
Rated voltage: no-load, rated, end voltage value (i.e. primary and secondary side voltage value);
No-load loss: under no-load conditions, the loss of the transformer (also known as iron loss);
No-load current: the current value flowing through the primary side coil under no-load conditions;
Short-circuit loss: the rated current of the primary side pass, the loss caused by the secondary short-circuit (mainly caused by the coil resistance);
Tap (tap) concept: In order to meet the operation needs of the power grid, the general transformer high voltage side has taps, and the voltage value of these taps is expressed as a percentage of the rated voltage, that is, the so-called tap voltage. For example, a high-voltage 10kV transformer has a ±5% tap, which means that the transformer can operate at three voltage levels: 10.5kV(+5%), 10kV (rated), and 9.5kV (-5%). In general, the number of taps (contacts) of on-load regulator transformers is more, such as 7 contacts (±3×2.5%) and 9 contacts (±4×2%). Since the synchronous switching of the tap-changer can not be fully guaranteed, the on-load voltage regulator generally cannot run in parallel.
9. PT (TV) /CT (AV)
The transformer is actually a special transformer, which is mainly used to isolate the primary circuit from the control circuit electrically, so as to expand the use of the secondary equipment (instruments, comprehensive insurance, etc.).
The use of PT/CT can avoid the high voltage/high current of the primary circuit directly into the secondary control equipment (such as: instruments, comprehensive protection devices, etc.), and can also prevent the failure of the control equipment from affecting the operation of the primary circuit.
The characteristics of the current transformer (CT, AV) are: the primary side winding N1 is thick and less, the secondary side winding N2 is thin and more, and the rated current I2 on the secondary side is generally 5A (according to N1I1 = N2I2, the primary side current I1 can be approximately calculated, or the current transformer with the corresponding ratio can be selected according to the primary side current I1). Since the primary and secondary winding of CT are in series in the primary loop and the secondary control loop respectively, according to the characteristics of the transformer U1I1 = U2I2, the working voltage of the secondary side at work, the voltage is very large in the open circuit, so CT is absolutely not allowed to open the circuit. By use, it can usually be divided into protective and measurement CT. The measuring CT is easy to saturate when the primary circuit is short-circuited, so as to limit the excessive secondary current (secondary winding side current I2) and to protect the integrated protection device. In order to ensure the reliable operation of the integrated protection device, there should be no protection phenomenon when the primary circuit short-circuit fault occurs.
The characteristics of the voltage transformer (PT, AV) are: the number of turns in the primary winding N1 is more, the number of turns in the secondary winding N2 is less, which is equivalent to a step-down transformer (the rated voltage on the secondary side is generally 100V). Since the primary winding and secondary winding of PT are in parallel with the voltage coil of the primary loop and the secondary control loop respectively, the current on the secondary side of PT is very small due to the large impedance of the voltage coil, and the secondary winding is approximately in the no-load state. However, the impedance of the secondary winding itself is very small, so if the secondary winding is short-circuited, it will lead to a very large secondary current (N1I1 = N2I2). Therefore, the secondary winding of PT must not be short-circuited.
10. Handcart/Drawer:
The handcart and drawer are part of the high voltage switch cabinet and the low voltage switch cabinet respectively, and the high voltage circuit breaker and the low voltage circuit breaker and their relays are installed respectively. Thus divided into car type switchgear (high voltage) and drawer type switchgear (low voltage), they and fixed switchgear function is basically the same, the main difference is to facilitate maintenance and repair (handcart and drawer can be promoted by mechanical operation mechanism crank, pull out). The handcart and drawer generally have three position states: work (normal operation), test (trial operation and field test) and exit (maintenance and overhaul).
11. Ground knife
Grounding knife (also known as grounding switch) mainly: first, it is used to ensure the safety of personnel when the line and equipment maintenance, grounding; The second is that it can be used to artificially cause the grounding short circuit of the system to achieve the purpose of control and protection.
The first function is easy to understand, no introduction. The second effect is this: The grounding knife is usually connected to the high voltage side of the buck transformer, when the fault occurs at the electric end or the internal fault of the transformer, the grounding knife switch should be automatically closed, resulting in a grounding short circuit fault, forcing the power supply end (upper end) circuit breaker to act quickly, cut off the fault, so this is a man-made grounding short circuit fault, the purpose is to ensure that the circuit breaker at the power supply end can act quickly.
12. Main electrical appliance
The master electrical appliance is a mechanically operated control appliance, which issues control instructions to various electrical systems for the conversion and transmission of various signals in the system, etc. The commonly used transfer switches, buttons, rotary switches, position switches and signal lights belong to the scope of the master electrical appliance.
13. Contactor
Contactor is a kind of electrical apparatus used for frequently switching on and off AC-DC main circuit and large-capacity control circuit at a distance. The main control object is motor, lighting, capacitor bank, etc., which is divided into AC contactor and DC contactor. Compared with circuit breakers, the difference is that the operating frequency is very high (so its electrical and mechanical life is required to be long enough); There is a higher breaking and switching capacity, but it is generally used in the voltage level of 1kV and below, which can not be compared with tens of thousands of volts and hundreds of thousands of volts of circuit breakers.
14. Relay:
Relays are used to control the action of other electrical appliances (generally primary electrical main equipment) in the control loop or as protection in the main circuit and for signal conversion. They are only suitable for long-distance breaking and connecting small-capacity control circuits, such as AC/DC current relays, voltage relays, time relays, intermediate relays, thermal relays, etc.
15. Experiment
Common tests include:
Type test: A test performed on one or more devices or equipment manufactured according to a design requirement to verify that the design requirement meets certain specifications.
Routine test: Also called factory test, a test performed on each device or equipment during manufacturing or after completion to determine whether the device or equipment meets a certain standard.
Dielectric test: is a general term for testing the electrical characteristics of the medium, including: insulation, static electricity, voltage resistance, etc.
Sampling test: The test of a number of samples randomly selected from a batch of products is also used to determine whether the sample meets a certain standard.
Life test: A test to determine the possible life of a product under specified conditions, or a test to evaluate and analyze the life characteristics of a product, is a destructive test.
Endurance test: Tests performed on products under specified conditions, such as repeated operation, short circuit, overvoltage, vibration, shock, etc. for a certain purpose within a certain period of time, are destructive tests.
Commissioning test
