Easy-to-control products are a cost-effective solution for power distribution monitoring systems in factories

Summary:As a part of factory automation, the factory power distribution monitoring system has been paid more and more attention by the top management of the factory to improve the intelligence of factory power distribution and ensure the reliability of power consumption. This article provides an effective reference for the management of the factory by introducing a cost-effective power monitoring scheme for factories.

Key words:Factory power distribution monitoring system, RTU, microcomputer motor protection

1 Introduction
The essence of factory power distribution monitoring is SCADA system (data acquisition and monitoring and control system), which is mainly composed of monitoring center computer master station system, communication channels and various remote terminal units on site (ie RTU, English name Remote Terminal Unit), right Remote monitoring, control and protection of important electrical appliances and power supply circuits in the factory, that is, to complete the comprehensive automation of the “four remote” functions and protection of remote signaling, remote measurement, remote control, and remote adjustment, and improve factory management by connecting with the factory MIS system. level of automation.
Factory power distribution monitoring includes:
1. Measurement of electrical parameters such as three-phase voltage, three-phase current, active power, reactive power, frequency, power factor, integral electrical degree, etc. of the high-voltage incoming line of the factory-provided substation, determination of the position of the circuit breaker, and remote control of the circuit breaker.
2. Discrimination of the temperature and gas signal of the transformer in the factory-owned substation.
3. Measurement of electrical parameters such as three-phase voltage, three-phase current, active power, reactive power, frequency, power factor, integral electrical degree, line harmonics, etc., remote control.
4. Three-phase voltage, three-phase current, active power, reactive power, frequency, power factor, integral electrical degree and other electrical parameters measurement of high-voltage motors, overcurrent protection, unbalance (negative sequence overcurrent) protection, grounding (zero sequence overcurrent) protection, long starting time protection, stall protection, inverse time overload (thermal overload) protection, undervoltage protection, overvoltage protection, temperature protection, motor thermal model protection, fault range discrimination, motor remote start and stop .
5. Measurement of electrical parameters such as three-phase voltage, three-phase current, active power, reactive power, frequency, power factor, integral electrical degree, etc. of low-voltage motors, overcurrent protection, unbalance (negative sequence overcurrent) protection, grounding (zero-sequence overcurrent) protection sequence overcurrent) protection, long starting time protection, stall protection, inverse time overload (thermal overload) protection, undervoltage protection, overvoltage protection, fault range discrimination, motor remote start and stop, forward and reverse rotation and delta star convert.
6. Measurement of electrical parameters such as three-phase voltage, three-phase current, reactive power, frequency, power factor, integral electrical degree, etc. of low-voltage capacitors and remote switching of capacitors.

2 Structure of factory electricity monitoring system

Easy-to-control products are a cost-effective solution for power distribution monitoring systems in factories

3 Introduction of factory electricity monitoring system
The English name of RTU is Remote Terminal Unit, and the name TeleControl is now given by IEC. It is a remote data acquisition and control device. The STC series miniature RTU of Beijing Yikong Microgrid Company is a kind of miniature RTU device that meets the requirements of IEC, and its model STC is the abbreviation of Small TeleControl. The MDS series microcomputer motor protection of Beijing Yikong Micro-Network Company is based on the advanced single chip platform and mature motor protection theory. It is a cost-effective intelligent motor protection product integrating motor measurement function and protection function.
The monitoring center can choose power version configuration software or professional SCADA software to complete data Display, remote equipment control, data generation and report forms.
The following is a brief introduction to the RTU or microcomputer type motor protection used in the scheme:
1. Features of the STC-2 AC Sampling Micro RTU
There is no need for voltage and other transmitters, and the three-meter method directly and accurately measures three-phase AC voltage, three-phase current, three-phase active power, three-phase reactive power, frequency, power factor, zero-sequence current, integral electrical degree, etc. parameter, the inverter output can be measured.
●With 3 independent switch relay outputs, it can be used as remote control, trip or alarm.
●6-way switch quantity optical isolation input, can also be used as pulse quantity input.
●2-way DC input (0-20mA or 0-5V), can be connected to various transmitters.
●Two-way communication interface, support MODBUS protocol, support the hot standby of the master station.
●FFT algorithm, can calculate 0-31 harmonics.
2. Functions of MDS-1 Microcomputer Motor Protection
●In addition to the measurement function of STC-2, it also has a motor protection function.
●Inverse time overload (thermal overload) protection, unbalance (negative sequence overcurrent) protection, long start-up time protection, stall protection, grounding (zero sequence overcurrent) protection, undervoltage protection, overcurrent protection of three-phase asynchronous motor voltage protection.
●Three-phase motor rotor broken, bearing damage, insulation monitoring and other fault diagnosis functions.
3. Function of MDS-104 Microcomputer Motor Protection
●Three-meter method measurement accurately measures three-phase AC voltage, current, active power, reactive power, frequency, power factor, zero-sequence current, zero-sequence voltage and other electrical parameters, and the fast data refresh rate is 100 times/S.The measurement data is refreshed 25 times/S, and it can also be used as a two-table method. Negative sequence protection cannot be performed under the two-table method.
●With 4 independent switch relay outputs, it can be used as remote control, trip or alarm.
●6-way switch quantity optical isolation input, can also be used as pulse quantity input.
●4-way isolated DC input (0-20mA or 0-5V), which can be connected to various transmitters;
●2-way RS232/RS485 communication interface, support MODBUS protocol.
Three-phase asynchronous motor overcurrent protection, unbalance (negative sequence overcurrent) protection, grounding (zero sequence overcurrent) protection, long starting time protection, stall protection, inverse time overload (thermal overload) protection, undercurrent Voltage protection, over-voltage protection, fault range discrimination, etc.
●Three sections of the line are overcurrent protection, inverse time limit protection, automatic reclosing
●It is possible to know whether the current motor is running forward or reverse through the calculation of positive sequence and negative sequence current, so as to prevent the motor from burning due to phase sequence errors caused by power grid accidents.
4. Features of the STC-1 DC Sampling Micro RTU
●8-way switch relay output, can be used as remote control, trip or alarm.
●8-channel switch quantity optical isolation input, can also be used as pulse quantity input.
●8-channel DC input (0-20mA or 0-5V), can be connected to various transmitters.
● 1 standard 485 communication port, 1 RS485/232 interface, support MODBUS or other protocols, it is easier to expand.
●SMD installation, no external bus, high reliability and strong anti-interference ability.
●Clamp rail or screw fixing
5. Features of STC-101 Micro RTU
16-channel switch optical isolation input, support pulse counting, support AC and DC 0 ~ 400V input
●1 standard 485/232 communication port, support MODBUS or other protocols, it is easier to expand.
●SMD installation, no external bus, high reliability and strong anti-interference ability.
●Clamp rail or screw fixing
6. Features of the STC-112 DC Sampling Micro RTU
●4-way switch relay output
●8-channel switch quantity optical isolation input, can also be used as pulse quantity input.
●8-channel DC input (0-20mA or 0-5V), can be connected to various transmitters.
●2 isolated analog outputs, 0~10V or 0~20mA
1 isolated 485 communication port, 1 RS232 interface, support MODBUS RTU or ASCII or other protocols
●Clamp rail or screw fixing
●SMD installation, no external bus, high reliability and strong anti-interference ability.

4 System configuration

For high and low voltage lines, each power supply circuit can be monitored by an STC-2; for the comprehensive monitoring of high-voltage motors, MDS104 microcomputer type motor protection can be used; For power-on detection, STC-101 miniature RTU can be used; for a large amount of DC acquisition, STC-1 miniature RTU can be used; for output adjustment that requires analog quantity, STC-112 miniature RTU can be used.

5 Communication Protocol

Based on the principle of openness, the MODBUS protocol widely used in the industry is selected. The MODBUS protocol is an open protocol developed by MODICOM and supported by many manufacturers. Through this protocol, controllers can communicate with each other, controllers and other devices via a network (eg Ethernet), and it has become a common industry standard.
The RTU and microcomputer type motor protection in this scheme support a subset of the MODBUS protocol, and the main function codes are:
●Read Coil Status (read relay output)
●Read Input Status (read digital input)
●Read Holding Registers
●Read Input Registers
●Force Single Coil (set a single relay)
●Preset Single Register (set a single holding register)
●Force Multiple Coils (set multiple coils)
●Preset Multiple Registers (set multiple holding registers)
●Read General Reference (read file)
●Write General Reference (write file)
●Read FIFO Queue (read FIFO queue)

6 Typical applications

The following is a description of a typical 10KV/400V substation. The primary wiring diagram is as follows:

The configuration is as follows:
Each switch uses an STC-2 product. 10KV adopts 2-meter method, and 400V adopts 3-meter method to measure voltage, current, active power, reactive power, power factor, harmonics, etc. Each switch has two position signals, each isolation switch has one position signal, and each line also has one watt-hour meter pulse signal, which requires five digital inputs. STC-2 has six channels and one channel is reserved. The output of STC-2 switch value circuit breaker has 3 channels, which are used to control closing and tripping respectively, and 1 channel is reserved.
131 bus tie switch adopts 1 STC-2 to measure 10kv bus tie current, 431 adopts 1 STC-2 to measure 400V bus tie current.
Motor protection adopts MDS-104, measures voltage, current, power, reactive power, power factor, provides overcurrent protection, unbalance (negative sequence overcurrent) protection, grounding (zero sequence overcurrent) protection, start-up of three-phase asynchronous motor Long time protection, locked rotor protection, inverse time overload (thermal overload) protection, undervoltage protection, overvoltage protection, fault range discrimination, etc.
Capacitors can use STC-2 or MDS-104, STC-2 is only for measurement, and MDS-104 can be used for overvoltage protection of capacitors.
Due to the small scale of the main station of the monitoring center, an industrial control computer is used to connect various devices to form an RS485 network through an isolated RS232/485 converter. The software adopts domestic configuration software.

7 Conclusion

The whole system has good openness, easy expansion, easy maintenance, simple installation, low investment, and high cost performance. It is an ideal choice for system integrators. Intelligent monitoring.

The Links:   LQ6RA01 B150XG02-V1