Secondary circuits - cables and wires that form a system that connects automation, control, signaling, protection devices, measurements. Thus, the secondary system of the power plant is formed.
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Secondary circuits come in several varieties. So, they include voltage and current circuits. They are distinguished by the presence of devices for measuring indicators of current, power, voltage.
There is also an operational variety. It contributes to the transmission of current to the main actuators. Secondary circuits of this kind are represented by electromagnets, contactors, automatic switches, fuses, keys, and so on.
The current circuit that comes from the CT for measurements is most often used to power:
- Instruments that display and measure ammeters, wattmeters, varmeters, and so on.
- Protection relay systems: remote, against short circuits, against circuit breaker failure and others.
- Devices for regulating power flows, emergency automatics.
- A number of devices included in the alarm system orlock.
In addition, the current circuit is used when there is a need to power devices for converting alternating current into direct current, which are used as sources of operational current.
How they are built
Installation of secondary circuits is subject to a number of rules. So, each device can be connected to 1 or more current sources. This is determined by taking into account the power consumption, the desired accuracy, the length.
When it comes to a multi-winding transformer, the secondary circuit is an independent source of current. All secondary devices that are connected to the CT of one phase are connected to the secondary winding in a certain order. Devices and connecting circuits must form a closed system. It is impossible to open the secondary circuit of the current transformer if there is current in the primary. Therefore, circuit breakers, fuses are never installed in it.
Protection
In order to protect personnel when faults in the secondary circuit occur, for example, when the insulation between the primary and secondary structure is blocked, protective earths are installed. This is done at the points closest to the TT, on the clamps. The isolation of the secondary circuit is also important in the case when several CTs are connected to each other, and it is fixed at one point. Grounding is provided by a fuse-discharger, whose voltage rating does not exceed 1000 V.
Be sure to take into account the characteristics of the primary system, in particular, the ability to power bothline 2 bus systems. For this reason, the secondary currents from the CT, which is fed to the relay and primary connection devices, are added. But this does not take into account the differential protection of the busbars and breaker failure.
If the connections are currently not functioning, to be repaired, then the working cover is removed from the test block. This leads to the fact that the secondary circuits of the current transformers are closed and grounded. At the same time, the circuits that went to the protective relays must be broken.
About voltage circuits
Voltage circuits that come from voltage transformers are used to power:
- Measuring devices that indicate and record data - voltmeters, frequency meters, wattmeters.
- Energy meters, oscilloscopes, telemeters.
- Protection relay systems - remote, directional and others.
- Automated devices, emergency protection, power flows, blocking devices.
- The organs that control the presence of tension.
They are also used to power rectifier devices, which act as sources of direct operating current.
About grounding
Ground for protection is always inserted into the secondary circuit. This is done by combining the corresponding device with one of the phase wires or the zero point of the secondary system. Grounding is done at a point that is as close as possible to the VT clamp assemblies or next to its terminals.
In the wires on the exposedphase grounding on the secondary circuit, work on installing circuit breakers between it and the grounding point of the circuit breaker is not carried out. The terminals of the voltage transformer windings that have been grounded are not connected. The cores of the control cables are laid to their destination - for example, to the busbars. Do not connect the conclusions that have been grounded on different voltage transformers.
During use, a voltage transformer may be damaged, the secondary circuits with protection of which are connected to automation devices, measurements, and so on. Reserved to avoid damage.
If there is a double busbar arrangement, the VTs mutually back up each other when one of the transformers is taken out of service. If there are 2 busbar systems in the circuit, the voltage circuits are automatically switched from one system to the other when switching the connection.
Always exclude the possibility that the earthed circuits of both transformers will be connected. This is extremely important. Practice proves that if this happens, the operation of the protective relay system, automatic devices will be seriously impaired.
It is always necessary to ensure that the detachable contacts are in good condition, as well as for the secondary circuits of voltage, operating current, which depart from them.
Operational current
At the moment, operative current is often used in electrical installations. When constructing its circuits, they must be protected from short-circuit currents. For this purpose, a number of separate fuses are used, eitherswitches, in which there are additional contacts for signaling, they feed the devices of secondary circuits with operating current. It is best to use circuit breakers instead of traditional fuses. They cope with this role more effectively, as practice shows.
The operating current is supplied to the protective systems of the relay and the control of the switches by means of separate circuit breakers. This is never done in conjunction with the alarm and interlock circuits.
On power lines, voltage transformers from 220 kV, switches are fixed to the main and backup protective systems.
A d.c. control circuit always has features to monitor the insulation and also to help provide warning signals when the insulation resistance drops. In DC circuits, the insulation resistance is measured at all poles.
In order for the operation of the devices to be reliable, it is necessary to control the correct supply of the circuit with the operating current at each connection. The best way to do this is to use relays that give a warning signal when the voltage drops.
About the term
Technical literature often expresses the concept of "secondary transmission circuits" in different ways. Yes, it has synonyms. Often the same phenomenon is called secondary switching circuits. However, many experts consider such a replacement unsuccessful. The thing is that the secondary switching circuit rather refers to the processes of switching electrical circuits, because the term "switching" is the nameaction.
It is important to distinguish among themselves and a number of other concepts. Electrical energy is transmitted through primary circuits. Secondary circuits are most often used with auxiliary power supplies. Their voltage is 220 V or 110 V, the use of combined power supplies is often noted.
The concept of "secondary power transmission circuits" may include several of their varieties:
- DC;
- with alternating current;
- in current transformers;
- in voltage transformers.
It also includes several taverns with different purposes. To distinguish secondary power transmission circuits from their different sections, a number of special designations are used.
They are numbered, taking into account the polarity of the circuits. So, the areas of secondary power transmission circuits with positive polarity are denoted by odd numbers. If the polarity is negative, even numbers are used.
If we are talking about a secondary electrical circuit with alternating current, then they are denoted by numbers in order, not divided by parity. Sometimes letters are used along with numerical designations.
Features
In voltage transformers, which are placed in power plants or substations with a number of switchgear, relay boards and control boards are placed far enough apart, grounding them at a place remote from the voltage transformer. Because of this feature, it is impossible to install circuit breakers that would protect the transformer in the event of a circuit short circuit.
Secondary circuit powered bycarried out using a battery, has some nuances. They are always taken into account when choosing fuses.
The concept of "secondary circuits" refers to wires and cables, including connecting equipment designed to measure quantities in the primary circuit.
They are used in pouring and pouring taps that work with liquid metals. Also used in high-speed cranes. In both cases, the circuits are wires with copper conductors, as well as with heat-resistant insulation.
It is important to consider that the fuses must be open in order to easily inspect and repair them without lowering the voltage on the entire assembly.
The circuit consists of insulated wires, combined into streams. If there are more than 25 wires in one stream, then working with them becomes excessively difficult.
Each stream is placed along the shortest path, placing it in a horizontal or vertical direction. It is permissible to deviate them from these positions by only 6 mm in each meter of length. Forming streams, the wires never cross. Each branch is drawn at right angles. It is important that their rows are even. Usually 10-15 wires are taken per stream. The bottom rows have the longest wires, while the top rows have the shortest.
If the secondary circuit in cabinets and panels includes copper wires, then in external connections - between cabinets and panels - control cables. Sometimes the external connection is implemented using wires in steel pipes.
In engines
It is not uncommon for questions regarding the secondary ignition circuit tooccur to motorists. The ignition system in a car ignites the combustible mixture in the engine at the right time. It helps to change the ignition timing, taking into account the load on the engine.
The ignition coil system consists of a primary and secondary ignition coil circuit.
Sometimes a car owner needs to check the ignition coil. It ensures the operation of the whole system, creating a spark between the candles. Many engines have only one coil, but sometimes there are two.
It is the coil that is the voltage transformer, turning it into thousands of volts. The secondary voltage produces a spark in the gap of the spark plug electrodes. Its indicator is determined by the gap, electrical resistance of the spark plug, wires, fuel composition, engine load. The maximum voltage is 40000 V, it changes frequently.
Working principle
The coil has 2 windings wound on a metal core. Primary with hundreds of turns and 2 external contacts of the coil are interconnected. Its positive terminal is connected to the battery, and its negative terminal is connected to the ignition module and body ground.
There are thousands of turns in the secondary circuit, it is connected with the positive pole to the primary, and the negative pole to the terminal in the center of the coil.
The number of turns in the other circuits is 80:1. As the proportion increases, the coil voltage at the output also increases. The highest powered coils have the highest proportion of turns.
When the primarythe winding is closed to ground, an electric current is started. So, by means of the appeared magnetic field, the coil is charged.
Next, the ignition modules open the primary circuit. Then the field suddenly disappears. A lot of energy remains in the coil, and it transfers the current to the secondary circuit. The voltage can increase more than a hundred times. At this moment, a spark "runs" through.
Faults
Ignition coils are reliable, durable devices. But sometimes there are also malfunctions. So, among the reasons for the appearance of defects are overheating, vibration. This leads to damage to the windings, insulation failure, resulting in a short circuit, and the circuits are interrupted. The biggest danger for them is overload, which is caused by damage to candles or high-voltage wires.
When spark plugs are damaged, too much resistance occurs in them. The voltage in the coil may increase up to the formation of breakdowns in the insulation.
Insulation may be damaged if voltage reaches 35000V. When this value is reached, the voltage decreases, misfire occurs under loads, the coil will not provide enough voltage to run the engine.
When a battery is connected to its positive terminal, and when shorted to ground, no spark is created - this is a sure sign that the coil is completely out of order and must now be replaced.
Diagnosis
When a problem appears in the ignition system, which is attributed todistributive type, it affects all cylinders of the engine. Its launch turns into a very difficult task. When the engine is running, but sometimes it misfires, and the “Check Engine” lamp lights up, then the time has come to use a diagnostic scanner. With it, they check the code that is associated with a misfire.
However, such a problem may be related to fuel failures, for this reason it is impossible to immediately accurately diagnose a malfunction in the coil, candles or high-voltage wires.
And here the knowledge of primary and secondary circuits is important. If there is no corresponding stake, then the resistance in the circuits must be measured. To do this, use a digital multimeter. It is important to see what condition the spark plugs are in, what is the gap between the contacts. Often, a malfunction is indicated by the color of soot on candles. Probably, the pass appeared due to the presence of oil deposits, strong soot. It is important to inspect the high-voltage wires to make sure that the resistance in them is within the specified range.
When it is established that the coil, its circuits are normal, it can be assumed that the fuel injector is dirty or damaged. So be sure to check it out. When the probability of its malfunction is excluded, then the compression is subjected to checks, the valves are checked to see if the cylinder head gasket has leaked.
But if the engine cranks and there is no spark, then the problem is probably in the control circuit. Verification is carried out guided by a number of strict rules.
Warning
In no case should you disconnect high-voltage wires from spark plugs or coils to check for sparks. The risk of electric shock is extremely high. In addition, there is a chance that the secondary voltage will severely damage the device. Therefore, if the need arises in this procedure, testers for candles are used, as well as a probe.
If there is a problem in the coil, then measure the resistance in both windings using an ohmmeter. When deviations from normal indicators are detected, the coil is replaced. It is also checked using an ohmmeter with 10 MΩ input resistance.
To test it, connect the test leads to the contacts in the primary circuit. Most often, the resistance ranges from 0.4 to 2 ohms. If a zero level was detected, then this is a sure sign that a short circuit has occurred in the coil. If the resistance turned out to be high, then the circuit broke.
Secondary resistance is measured between the positive terminals and the high voltage terminals. Modern devices most often have a resistance of 6000-8000 ohms, but sometimes there is also an indicator of 15000 ohms.
In other types of coils, the primary contact may be located in the connectors or be hidden.
Danger
If you don't apply what you learned and leave the coil defective, it will one day damage the entire PCM unit. The thing is that the reduced resistance of the primary circuitleads to an increase in current in the coil. Therefore, the chances that the PCM unit will break increase.
Also, the secondary voltage may also decrease, and the sparking will weaken, starting the engine will be accompanied by many difficulties, misfiring will occur again and again.
The increased resistance of the secondary winding provokes the weakening of sparks in the cylinders, strong self-induction in the primary circuit.
Replacement
The coil can only be replaced with a similar one in cases where there are no plans to improve the ignition system. Be sure to pre-clean each contact and connection in it, look for signs of corrosion on it, check how reliable the connections are. The thing is that corrosive processes lead to an increase in resistance in an electrical conductor, instability of the connection, and breakage. All this significantly reduces the life of the coil. To reduce the likelihood of breakdowns in conditions of high humidity, dielectric candle grease is used on the contacts of the coil.
When the engine has a problem, the coil is in the most severe conditions. A fault provokes a high secondary resistance. So, the candles may wear out or the gap between the electrodes may be too large.
If the mileage is large enough, then simultaneously with the new coil, the installation of new candles is also carried out.
Installing the secondary circuit
To perform this operation, you need to familiarize yourself with many features of the layout of streams. Experience is required to properly install the secondary circuit. Finitethe result will largely depend on the correct layout, execution of threads.
Before starting the installation, the specialist gets acquainted with the installation, and sometimes the circuit diagram. Then he determines by what method he will lay, arrange the wire flows. There are a number of rules in this procedure. So, the wires that belong to 1 mounting unit are connected in one thread.
Also remember that a large number of wires will require more work on them. Never lay wires in such a way that they cover the contacts of devices, part of the fasteners.
When laying many layers of threads, do not lay more than 10 wires in one row at once. Wires of one row are connected to adjacent contacts of devices or clamps. The wires that are laid between the connections are always intact. In no case should you splice them.
The appearance of each thread will depend on how the wires are prepared. If the amount of work is small, then the preparation of the wire will be to cut it to the desired length and trim it.
Laying methods
There are several ways to mount the secondary circuit. If non-standard panels are made, then most often they do this by laying the wires directly. For installation in this way, you will need a panel made in a suitable way for this. If it has equipment to connect the wires from the front, then at a distance of about 40 mm from the clamps, a series of holes is drilled, the diameter of which is 10.5 mm. A U-457 type bushing is inserted into each. Type-setting clips are placed on the front side. The same holes are made in the clamps and bushings are inserted. Wires are placed on the back side of the panel. They are brought out through the bushings to the front side.
Before connecting the wires coming from the sleeve, they are bent into a semicircle, creating a compensator. They are also pulled as tightly as possible, which allows you to create a more aesthetic appearance on the other side of the panel. The longest of them are fastened with mounting tapes. Wires that run in the same direction do not need to be tied together.
There is another method of fastening - using Loskutov strips. For this, laying lines are preliminarily drawn. When fastening with a wire is carried out using staples, holes are also made, threads are cut. For the manufacture of staples, sheet steel is taken, whose thickness is about 0.7 mm. Their size will depend on the number of thread wires.
Usually, the wires are fixed using strips of sheet steel, which are welded to the panels by spot welding using the Loskutov method. The distance between them is 150-200mm.
Some areas of the route are subdivided into several equal intervals. Welding is carried out in 2 - 4 points. An insulating electric strip is laid along the route. Also, insulation pads are placed between wires with stripes.
Streams with wires are pulled together by strips that are passed through buckles. The ends of each strip are folded over, and the excess is trimmed.
Laying wires in streams goes like this:
- Cutting the wires, they are laidinto the thread, and then connected to the clamps of the devices.
- Be sure to ensure that there are no deviations from the horizontal and vertical position.
- If the track is chosen correctly, the lines are straight, then the device has a pleasant appearance.
- The bending of the wires is carried out in such a way as not to harm their insulation. For this reason, the bending radius must be at least 2 times the outer diameter of the wire. The bending is done by hand, never bending the wires again. Lay them out tight.
