# motor control circuit

Starting a three-phase induction motor is as simple as applying full power to the stator windings. Not only can motor winding temperatures be monitored, but also bearing temperatures and other temperature-sensitive machine components so that the protective function extends beyond the health of the electric motor. The only “wearing” components are the bearings supporting the rotor shaft, and those are easily replaced. In the forward-control circuit, a normally-closed auxiliary contact actuated by the “reverse” contactor is wired in series, and vice-versa in the reverse-control circuit. A capacitor-start, single-phase electric motor is shown in the following photograph. Motor control Timer relays are covered too. All industrial training software shown here is Win 10 to XP compatible. If the control circuit transformer primary is tapped from the motor circuit and the control circuit leaves the controller enclosure, and is less than 50 volts, it must be grounded if: Both fuses and circuit breakers tend to be fast-acting devices, intended to interrupt overcurrent resulting from an electrical fault such as a phase-to-ground short circuit. With microprocessor technology comes vast increases in responsiveness and precision of timing, as well as digital networking capability to share system data among other components and to human operators. That lever connects to a spring-loaded mechanism charged by the manual actuation of the red “Reset” push-bar, which in turn actuates a small set of electrical switch contacts: The purpose of the overload heater is to heat up as the motor draws excessive current. Three-phase electric motors that become “single-phased” from a fault in one of the three-phase power lines will refuse to start. This next photograph shows a digitally monitored and controlled “bucket,” using DeviceNet as the control network: Using a digital network standard such as Ethernet, DeviceNet, Modbus, Profibus, or any number of others to monitor and control a motor brings a host of benefits for maintenance and operations. Thus, this simple mechanism prevents the overloaded motor from being immediately re-started after a thermal overload “trip” event, giving it time to cool down as well. Then you will be ready for the interactive quiz and to print your certificate when you make 85% or better. Manually pressing the “Reset” push-bar will re-set the spring mechanism and re-close the overload contact, allowing the contactor to energize once more, but only once the overload heater element has cooled down enough for the solder inside the brass cylinder to re-solidify. This is called a capacitor-start induction motor, and it is the design used for most single-phase AC induction motors requiring a high starting torque (e.g. Training Applications for the Electrical Controls Industry, [Video below shows Electrical Motor Controls Training software in use.]. It may come as a surprise for some to learn that any conductive object – ferromagnetic or not – will experience a torque when placed inside the rotating magnetic field generated by the stator coils. A contactor rated at 75 horsepower (at 480 volt AC 3-phase power) is shown here, both assembled and with the top cover removed to reveal the three sets of high-current electrical switch contacts: Each phase switch contact is actually a series pair of contacts that make and break simultaneously with the actuation of a ferrous armature attracted by an electromagnet coil in the base of the contactor assembly. ELECTRICAL CONTRACTOR? This “amplifying” action enables relatively small control switches, PLCs, and relay circuits to start and stop relatively large (high-current) electric motors. AC Motors simplified with interactive demonstrations. By measuring the voltage dropped across each overload heater (with the motor running), one may ascertain whether or not all phases are carrying equal currents. In an automatic control system, the toggle switch would be replaced by another relay contact (that relay controlled by the status of a process), a process switch, or perhaps the discrete output channel of a programmable logic controller (PLC). This electric motor control circuit training software is quite detailed. If the transformer is rated not over 1,000 volt-amperes, a grounding electrode conductor not smaller than No. If the control circuit is supplied through a transformer, then it is a "separately derived system" as defined in Article 100, and could be grounded as required by Sec. After all, this is precisely how three-phase electric power is generated: by spinning a single magnet at the center of three sets of coils offset by 120 degrees. A programmable logic controller (PLC) may also be used to provide the latching function rather than an auxiliary contact on the contactor. the MCC room lacks air conditioning while the motor is located in a freezer), they may “trip” the motor prematurely. If the rotor ever did achieve synchronous speed, there would no longer be any relative motion between the rotor and the rotating magnetic field, which means the induction would cease. If both contactors were to be simultaneously actuated, it would result in a direct phase-to-phase fault (short-circuit) between L1 and L3! To start up and shut down a three-phase AC induction motor, any three-pole switch with a suitable current rating will suffice. Don't worry, we'll come to you. Induction motors are by far the most popular design in industry. My hand is touching the capacitor enclosure for the motor’s starting winding. If the magnetic field completes one full revolution in $${1 \over 60}$$ of a second, the rotating speed of the magnet will be 60 revolutions per second, or 3600 revolutions per minute (3600 RPM). Although the electric motor may operate on three-phase, 480 volt AC power, the contactor coil and the rest of the control circuitry operate on a lower voltage for reasons of safety. Watch demonstrations while the electrical motor circuit is simulated. If an electrically conductive object were placed within the center of this same machine on a shaft such that it was free to rotate, the relative motion between the rotating magnetic field and the conductive object (rotor) would induce electric currents in the conductive object, producing magnetic fields of their own. (1) the transformer primary supply system exceeds 150 volts to ground, The fact that all AC induction motors must start as polyphase machines even though they can run as single-phase machines means that an AC motor designed to run on three-phase power may actually continue to run if one or more of its phases are “lost” due to an open wire connection or a blown fuse. SCHWAN is an electrical code consultant in Hayward, Calif. A three-phase motor, however, cannot start from a stand-still on just one phase of AC power. A typical “two-pole” induction motor operating at a power line frequency of 60 Hz has a synchronous speed of 3600 RPM (i.e. If we have only one sine wave supplied by the AC power source, is it possible to generate a truly rotating magnetic field? [250-20(b)] [90-7 ¶ 2, 300-1(b), 450-1 Exc.No.2] If, however, a ground fault develops within the motor where some AC current “leaks” from a stator winding to earth ground to return to the 4160 VAC power source’s neutral connection, that imbalance of phase currents will be sensed by the zero-sequence CT, since that ground-fault current represents the fourth path for current not accounted for by the three power conductors passing through to the motor. Preplanned Post-Installation Inspections: Do you need periodic testing of water features after the work is complete. [250-21] (1) it can be grounded so that the maximum voltage to ground does not exceed 150 volts, or (The entire course is narrated too.). (2) the transformer primary supply system is ungrounded, or The overload heaters appear in the schematic diagram as pairs of back-to-back “hook” shapes, connected in series with the three “T” lines of the motor. Others are in-direct motor control sensors like the limit switch and the proximity  switch. An essential component of any high-power motor control circuit is some device to detect a condition of excessive overload and interrupt power to the motor before thermal damage occurs. All rights reserved. (3) ground detectors are installed on the control circuit.

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