A switchgear system that is capable of handling between 3kv and 36kv is referred to as medium voltage switchgear. These come in many types, such as metal-enclosed outdoor type, metal-enclosed indoor type, as well as an outdoor type without metal enclosure, among others.

MNS is ABB’s low-voltage switchgear and controlgear assembly for power distribution and motor control. The MNS design is verified in accordance with the latest IEC standards, IEC 61439 -1/-2 and IEC TR 61641.

IEC 61439 standard follows the philosophy of IEC 60947 series i.e. IEC 61439-1 is ‘General Rules’ standard to be referred to by subsidiary product parts of IEC 61439 series….Introduction to IEC 61439.

All three contain circuit breakers. All three supply power to motors, although switchgear and PDC-fed motors are obviously higher-voltage, larger motors. Switchgears are higher voltage than PDCs, and supply power to the transformers which feed the PDCs. PDCs are higher voltage than MCCs, and supply power to MCCs.

A motor control center is in general a Controlgear in the IEC terminology and can be confused with a switchgear. Therefore a MCC cannot be considered as a switchboard because switchboards are supposed to contain circuit breakers only and not motor contactors (IEC terminology) or motor controllers (USA terminology).

motor control center

A MCC can include variable frequency drives (VFDs), programmable controllers, and metering and may also be the electrical service entrance for the building. Motor control centers are used in the factory assembly of several motor starters. Feeders are designed according to the motor rating.

MCC : Motor Control Center or Substation where motor will be powered. PLC/DCS : Control System, where Motor can be controlled as per logic (Auto) or as per operator action (Manual).

The VFD Panel (Variable Frequency drive panel) also known as VFD Control Panel are designed to control the speed of electric motor and feed pump. They are widely used in drilling, pumping and other large machine applications.

The most common uses of a VFD are for control of fans, pumps and compressors, and these applications account for 75% of all drives operating globally. Soft starters and across-the-line contactors are other, less sophisticated types of motor controllers.

A function that automatically controls the output voltage by detecting an output current of an Inverter to increase the torque when it is insufficient. The automatic torque boost enables relatively powerful operation of a motor even in V/f control.

Thus, the rule of thumb for sizing the single phase input on a three-phase drive is to use a VFD rated for 2 times the FLA of the motor. For example if your motor is a 10 HP motor with a FLA of 28 amps, then you would need to select a VFD with an amp rating of 56 amps which ends up being around 20 HP.

In low voltage VFDs, we think the best VFDS on the market are the WEG VFD, the Yaskawa VFD, the Toshiba VFD, the LSIS VFD, and the Teco VFD (especially in the high horsepower low voltage models) All of these are good companies with well designed reliable equipment.

VFD sizing should always be based on motor current and voltage, not hp. Let’s begin with the basics by learning how to read a motor nameplate. The nameplate in Figure 1 shows that motor current is based on the input voltage: volts (V) 230/460, full load amps (FLA) 13.4/6.7.