Abstract: Most of the chemical plants have high requirements for power supply and are continuously produced. Sudden power failure and rapid restoration of power supply may cause explosions, resulting in personal injury and death, equipment damage, and difficulty in repairing, or production. Polymerization and other phenomena produce a large amount of waste products, causing full-line parking, which brings significant economic losses to the enterprise. Therefore, it is necessary to set up a reliable standby power supply automatic input device according to the engineering needs to improve the reliability of power supply and reduce major economic losses.
Keywords: reliability  Automatic backup power supply  Interlocking
Most of the chemical plants have high requirements for power supply. Most of the electrical equipment is secondary load, and some devices have a small part of the primary load. Chemical companies generally produce continuously, and suddenly the power is cut off. The restoration of power supply will likely cause an explosion, resulting in personal injury, equipment damage, and difficult to repair, or production polymerization, production of a large number of waste products, resulting in full-line parking, bringing significant economic losses to the enterprise, therefore, the power supply Reliability puts higher demands on it.
In order to solve this problem, the chemical equipment is generally dual-circuit power supply. In normal time, the two channels are simultaneously powered, and each other is used for standby. The equipment is automatically powered by the power supply unit ( BZT ). When one of the power sources fails, BZT is put into the other way. The power supply will carry all loads, or primary and secondary loads, and the automatic restart link will be used to meet the requirements of continuous production. For the first-level load that requires higher power supply reliability, only UPS , EPS or diesel generators are used to meet the requirements for power supply reliability.
The continuous development of modern power technology also requires the installation of various automatic devices in substation equipment. The main functions of these automatic devices in substations are as follows:
1. Â Ensure reliable power supply and eliminate inaccurate or erroneous actions that may occur when an operator performs an operation.
2. Â Reduce the labor intensity of the operating personnel or replace the activities of people and increase labor productivity.
3. Â Ensure the safe and reliable operation of electrical equipment, so that the operating personnel can accurately and accurately judge the abnormal situation during operation and deal with it in time.
Automatic devices should be reliable, selective, sensitive and quick-acting. How to use the electrical interlock to achieve the above requirements, and to prevent power outages caused by human error in the sequence of operations is the focus of this article.
First, the basic way of BZT
In the power supply system of chemical enterprises, BZT generally has two basic methods:
1. Â Â Â Â Â Â Â Â Â Â With a normal working line and a hot standby line, the BZT device controls the incoming switch of the hot standby line. When the normal working line fails and is cut off, the standby line is automatically put into operation, so-called single-direction BZT . The security power supply for chemical plants is generally used in this way.
2. Â Â Â Â Â Â Â Â Â Â A substation with two independent working lines, the BZT device controls the segmentation switch of the busbar. When normal, the segmentation switch is disconnected. When any one of the working circuits fails and is cut off, the segmentation switch is automatically input, and the other segment is automatically The line is for full load, or primary and secondary loads, the so-called two-way BZT . Substations of chemical plants are generally used in this way.
Second, the standby power supply automatic input device wiring requirements
1. Â Ensure that the backup power supply is put into the standby circuit after the voltage and working circuit are disconnected.
2. Â When the voltage on the working circuit disappears for any reason, the automatic input device should delay the action.
3. Â When the working circuit is manually disconnected, the automatic input device is not activated.
4. Â The closing pulse of the standby power circuit breaker should be short pulsed, and only the automatic input device is allowed to operate once.
5. Â After the standby power supply is automatically put into operation, the fault is applied to the fault, and if necessary, the protection should be accelerated.
6. Â The standby power supply is automatically put into the device, and the current blocking circuit of the working power source can be set.
7. Â A standby power supply self-injection device equipped with synchronous check or low voltage start, in order to prevent the BZT from being blown by the secondary side fuse of the voltage transformer of the working power source or other reasons , a signal or blocking device should be provided.
8. Â In order to let the operating personnel know the working status of the working power supply and the standby power supply in time, the necessary signals should be set, such as the standby power supply no voltage signal.
9. Â For a BZT device with a low-voltage start , when the operating power supply voltage drops or disappears, and the voltage on the power busbar drops or disappears, and the standby power supply bus maintains a certain voltage value, the automatic device is allowed to start.
Third, the composition of the 6kV automatic switching system
The system consists of a low-voltage detection and starting device and a standby power supply automatic input device. This article focuses on the difference from the previous system, that is, adding a voltage transformer on the power supply side and the bus line, and adding more on the power supply side. The voltage transformer can be used to monitor the power supply side voltage and start the standby power supply automatic input device as a low voltage detection. The detailed interlocking principle of the system is shown in the following logic requirements for the main switch operation principle.
Different from the previous system, there are two more selection switches in the system introduced in this paper. One is automatic and manual selection switch. When the switch is in the automatic position, the BZT device is put into operation. When the switch hits the manual position, the BZT is Lifted. Another selector switch is the trip position selector switch, which has three positions: Incoming Line A Trip, Incoming Line B Trip, and Bus Trip. The detailed application is described below.
1. Â Â Â Â Â Â 6kV substation automatic switching system logic diagram
This figure is drawn according to the power supply B fault. See Figure 1 .
It can be seen from the figure that under normal operation, when a low voltage appears on the power supply B side, and the overcurrent protection does not operate , or the incoming line B switch is turned on, and the overcurrent protection does not operate, in this case, It is further confirmed whether the B- segment busbar also has a low voltage, and the bus voltage of the A- segment busbar is normal, so as to avoid unnecessary switching due to the low voltage misoperation of the B- segment power supply. If all of these conditions are met, skip the B- stage incoming switch and combine the bus-coupled switch.
2. Â Â Â Â Â Â 6kV substation restores two-way power supply logic diagram
After the power supply of the faulty section is restored, if the two lines supplied to the substation allow short-term paralleling, the design according to the logic diagram shown in Figure 2 can complete the recovery of the two ways without stopping the power of the process equipment. Power supply switching.
As can be seen from the figure, the feature of the figure is that the trip selection switch 43S is more than the previous standard diagram. When the switch is hit to the tripod trip position, it is electrically ensured that the line switch must be first engaged. After the jumper bus switch, to ensure continuity of power supply. This also avoids the fact that in the past, due to the work ticket and the operating procedure to perform the switching operation, human error may occur during the operation, which causes unnecessary loss to the production.
3. Â Â Â Â Â Â 6kV substation maintenance switching logic diagram
When it is necessary to repair one of the incoming line switches, and then do not want to interrupt the power supply, then according to the logic diagram shown in Figure 3 , it can ensure that in the case of the process device without power failure, the switch to the first loop power supply, maintenance Incoming switch.
As can be seen from the figure, the main feature of the figure is that the trip selection switch 43S is more than the previous standard diagram. When the maintenance incoming line switch is to be performed, the switch is turned to the position where the maintenance line switch needs to be repaired, thus The interlock must ensure that the bus coupler switch must be connected before the jumper switch that needs to be repaired can be tripped, thus avoiding the mistakes that may be caused by human operation.
4. Â Â Â Â Â Â Manual operation logic diagram of 6kV substation
Any automatic device should be set to a manual operating position to facilitate maintenance and commissioning requirements. When manual operation should also meet certain conditions, a certain electrical interlock should also be added to prevent misoperation. As shown in the figure, when dual power supply is not allowed to be connected, the electrical interlock should be added as required in the figure.
It can also be seen from the figure that if the line switch is to be manually engaged, the line switch must be closed when another line switch is opened or the bus switch is turned on. That is, the protection link to prevent parallel operation is added. By the same token, if you want to switch the bus coupler, you must have one of the two incoming lines that is open.
Fourth, BZT 's action time and its selectivity
BZT action must be considered on time with lower levels of problem, if there is a higher level substation BZT, BZT this substation is the time to meet when setting higher success substation BZT, BZT this substation will not have to put requirements. The device with automatic restart motor must also shorten the BZT setting time to facilitate the automatic restart of the motor, and some chemical devices do not allow the power outage time to be too long, otherwise it is prone to explosions and other accidents. When there is a contradiction between the two, the safety production requirements of the process device should be ensured first, and the BZT setting time should be shortened . When the power supply is restored, the power supply is switched to the dual power supply.
In short, the BZT setting time should be considered comprehensively, that is, the electrical selectivity should be considered, and the special requirements of the process equipment should be considered, and a specific analysis should be made for each power supply device to develop an effective power supply scheme.
Reference material
1 . The third edition of the Manual for Industrial and Civil Power Distribution Design;
2 . "Code for design of relay protection and automatic devices for electric installations" GB50062-92 ;
3 . Electrical Engineering Electrical Design Handbook.Sewage Gas Generator,Propane Powered Generator,Hydrogen Generator,Gasoline Generator
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