Overview of Device

UNT-MMI intelligent MCC (Motor Control Center) control protection management device is the new-generation digital-type intelligent MCC control protection management device with strong interference resistance developed by Baoding UNT Electric Co., Ltd. after studying similar products in foreign countries and summarizing the typical design experience of a lot of MCC electric systems in China, which is based on the design characteristics of MCC circuit and for adapting to the intelligent trend of secondary equipment in electric system.

This product is mainly used in low-voltage motor control circuit, so as to achieve various protection, monitoring and control functions for motor, and achieve the remote monitoring on motor circuit via field bus.

UNT-MMI intelligent MCC control protection management device adopts the general design concept, realizes the control, protection, interlock, measurement and signaling function on secondary circuit on the basis of the simplified primary circuit (The protectors such as traditional thermal relay, thermal protector, undervoltage/overvoltage protector are deleted; and secondary elements such as time relay, intermediary relay, auxiliary relay, current transformer, instrument, changeover switch, indicating lamp and programmable logical controller are cancelled), is equipped with rich field bus interfaces, and complies with various communication protocols. The strong statistics & analysis function and management software enable the user to understand the operation of motor in a real time manner and find and settle various problems in time.

As a result, this device can greatly improve the efficiency of design and production, reduce the on-site adjustment and maintenance workload of user, shorten the design and commissioning period of project, and bring in obvious comprehensive benefits. UNT

Through many years’ engineering practices, UNT-MMI products have been widely used in power, chemical, paper-making, metallurgical, utility, coal and nuclear industries, and its operation is stable and reliable.

1.2 Features of DeviceWith the 32-bit industrial microprocessor adopted, the speed is high and the precision is also high. The true RMS algorithm is adopted for AC sampling, so as to fully reflect the impact imposed by harmonic wave current. The self-adapted frequency-changing sampling technology is adopted, which is suitable for frequency converter circuit. Several flexible control modes are available, and control authorities are interlocked. The device adopts the small-sized design, and the installation mode is flexible. Metal casing design is adopted, so that external electromagnetic interference is effectively shielded. The LCD based on Chinese characters and rich menu is adopted, and the interface is user-friendly. The switch quantity input circuit adopts the design of high interference resistance, so as to ensure long transmission distance and high reliability. The internal control contacts are equipped with protection circuit, and the contacts can be effectively protected without additional surge absorber. The device is equipped with memory chip, and the functions such as anti-voltage flicker function and self-starting function after recovery of voltage can be realized without installation of separate power supply module. The problem that the overload of thermal relay and MCCB can’t simulate the electric characteristic and thermal characteristic of MCC load is settled, the thermal relay is saved, the construction of MCCB is simplified, and the current-consuming equipment can be better protected. The problem that MCCB instantaneous tripper is not enough sensitive to motor-side single-phase earthing protection for long-distance power supply is settled, and it is unnecessary to install the single-phase earthing protection means for settling such problem. The perfect overload protection is provided. The thermal model has considered the comprehensive thermal effect of positive/negative sequence current of motor, and the heating and heat-elimination processes of motor is precisely simulated through heating constant and heat-elimination constant. Rich programmable logics are provided, so that the complicated interlock (such as interlock between motors, interlock between motor and physical quantity such as liquid level or temperature) can be realized and the efficiency of design can be improved. The device is internally equipped with the 4-20mA output interface which is electric-optical isolated, the output electric quantity is selectable, and the range is adjustable. The industrial field bus technology (Profibus-DP/ModBus/CAN) is adopted, which can quickly realize the connection with monitoring system and PLC communication devices and achieve the remote advanced management function. The double communication interface design can achieve the redundancy of networks and greatly improve the reliability of communication, and the network-forming mode is flexible. Strong statistics & analysis function (event record, and management record) enables the user to understand the operation state of motor in a real time manner. This device is equipped with special software, so that various set values and parameters of the device can be viewed and edited, the state of motor can be monitored in a real time manner, and the PLC can be realized. This device has passed the 15 electromagnetic compatibility inspection items carried out by National Relay Quality Supervision and Inspection Center, and the severity level is IV. This device has passed the inspection carried out by the National Explosion-proof Electric Product Quality Supervision and Inspection Center, and is suitable for safety-enhanced explosion-proof motor.

2.2 Control Function

The device has several control functions, and every function can be used to control the motor.

Control keys on panel Fixed input for device The connecting point of device for programmable input can be defined as the starting/stop control point for motorField communication bus

The four-site operations are mutually interlocked, which can be achieved by software-based setting or externally-installed changeover switch.

Perfect Starting Mode

Operation Mode
Plastic-casing breaker + contactor motor circuit	One-way operation
	Two-way operation
	Resistor-based voltage-reduction starting
	Star-delta starting
	Autotransformer starting
	Dual-speed operation
Framework breaker motor circuit	To control the operation mode of framework breaker

Complete Control Program

	Control Site					Changeover Mode
Two-site control	Local	Remote
	Low-voltage switch cabinet (device panel)	Operation box near machine				Software setting
						Externally-connected change-over switch
	Low-voltage switch cabinet (device panel)	DCS hard wired				Software setting
						Externally-connected change-over switch
	Operation box near machine	DCS hard wired				Externally-connected change-over switch
Three-site control	Local	Remote
	Low-voltage switch cabinet (device panel)	Operation box near machine		DCS hard wired		Externally-connected change-over switch
	Low-voltage switch cabinet (device panel)	Operation box near machine		Communication operation		Software setting
						Externally-connected change-over switch
	Low-voltage switch cabinet (device panel)	DCS hard wired		Communication operation		Software setting
						Externally-connected change-over switch
Four-site control	Low-voltage switch cabinet (device panel)	Operation box near machine	DCS hard wired		Communication operation	Externally-connected change-over switch

Self Starting Function after Recovery of Voltage

If the voltage of primary circuit recovers to normal level after being lost for short time, the device can recover the motor to the operation state before the loss of voltage. The self starting function after recovery of voltage can effectively settle the impact on operation of system caused by voltage loss or voltage flicker.

This function involves four parameters, which are detailed as follows:

Udrop: under-voltage

Tuv: under-voltage time

Upick: recover voltage

Tdly: starting delay

In the course of operation of motor, if the voltage of primary circuit is lower than Udrop, the device will stop the motor. If the voltage of primary circuit recovers to higher than Upick within the Tuv, then the device will recover the operation of motor after Tdly.

In addition, except for important load device which has DC power supply, many devices use AC power supply, and after the voltage of primary circuit is lost, the devices will also be deenergized, and will not judge the state of three-phase voltage of primary circuit. However, this device is internally equipped with memory circuit, and after the power supply for this device is recovered, this device can recover the initial operation state of motor.