Electric Motor Control

Calculate the full-load current for a 15 hp, 400 V three-phase motor by converting hp to kilowatts, dividing by efficiency, and applying P_in = √3 V I pf.

Apply the NEC rule of 125% of full-load current to select a cable for a 15 hp, three-phase induction motor, targeting a 24 A ampacity and a 225 mm² cable.

Learn to select overcurrent protection for a squirrel cage induction motor using the National Electrical Code, sizing circuit breakers and fuses with 125 percent continuous load and time-delay factors.

Select a circuit breaker for induction motor over current protection using 125 percent of continuous load and 250 percent of full-load current, choosing the lower standard rating not exceeding maximum.

Set motor overload protection with trip points at 125 percent of the followed current for service factor ≥ 1.15 or 40°C or less rise, otherwise 115 percent.

Select a contactor sized to 100 percent of the full-load current, here 19.15 A, using the manufacturer catalog; for a 400 V 3-phase motor at 50/60 Hz, 25 A.

Determine main feeder size using NEC: 125 percent of the highest motor current plus the sum of the other motors, then select a 50 mm² copper cable with BBC insulation.

Select the main circuit breaker to protect the main feeder against overcurrent, using 125 percent and NEC guidelines to determine size and appropriate cable and protective device settings.

Design a three-phase electrical power system with an oil pipe transformer, 400 V, 50 Hz, 5% short-circuit impedance, and 40 degrees Celsius ambient, size breakers and cables, and perform tests.

Select the proper transformer size based on load estimation and total connected load. Apply demand and diversity factors, assess voltage drop, and plan power factor correction, derating, and future growth.

Compare liquid immersive oil type transformers and dry type transformers, noting their tank and insulating liquid construction, indoor safety requirements, and oil type's lower losses and higher efficiency.

Explore how the transformer vector group defines winding configuration and phase angle, including delta and star connections, phase shifts between windings, and implications for paralleling to avoid circulating currents.

Explain transformer grounding in low voltage networks by bonding the neutral point to earth with high impedance, include resistors, reactors, and capacitors to manage fault currents.

Compute the full-load current from the transformer using three-phase power formulas, then select a circuit breaker at 125% of that current, yielding a 1600 A breaker.

Apply derating factors to determine the current rating and prevent insulation damage; compute I_kable as circuit breaker divided by derating factors and select a suitable 300 mm² copper cable.

Perform a voltage drop test using loop current, 50 meter cable length, and five parallel 300 mm2 cables, yielding a 4.5% drop at the main distribution board.

Calculate short-circuit current at the main distribution board using the impedance method, incorporating transformer and cable reactances, per-unit impedance, and system base power.

Learn practical wiring of a motor power circuit, connecting fuses, circuit breakers, contactors, and overload relays to a three-phase feeder, and identify device terminals for a proper induction motor setup.

Design a single motor control circuit with one-location start and stop, using a contactor with a latched auxiliary contact and overload protection to hold the motor after starting.

Wire the control circuit from a single location using pushbutton start/stop, the circuit breaker and overload relay auxiliary contact, and connect the contactor coil to terminals 95–96 and 11–14.

Turn schematic diagrams of power and control circuits into wiring for motor control, using horizontal layouts, color-coded cables, distinct control vs power colors, and cable markers with symbols and numbers.

Examine how the arrangement of devices and contacts, including the start and overload relay, controls a motor via the contactor latch, illustrated with a three switch simulation.

Learn to wire a motor indicator circuit with visual signal lamps, normally open and normally closed auxiliary contacts, a contactor, and lamps to show normal operation, disconnection, overload, and faults.

Examine the motor control circuit from the previous lesson, explain why the bailout lamp stays on when the motor is disconnected, and show overload trip behavior.

Wire the motor control circuit using stop and start buttons, a contactor, and overload relay; route the main coil through 95/96 and 97/98, with neutral.

Operate the power circuit and control circuit at different voltage levels, including ac voltages from 200 to 600 v and dc voltages from 12 to 60 v, as shown.

Connect a transformer to the 380 volt three-phase supply to obtain 220 volt ac on the secondary, select a primary line, and connect a neutral on the secondary.

Learn to start a motor from two switches and stop it from two switches using a latching auxiliary contact, series and parallel wiring, and overload protection.

Design a conveyor control circuit that energizes the main coil when load is present and start is pressed, using a limit switch to close normally open contacts and run motor.

Design automatic water pump control circuit using overload relay 95-96, fuse or circuit breaker, and selector switch; motor runs on low pressure, stops at high level, with overload protection.

Explore how a single motor uses a three-location start and three-location stop wiring, including series and parallel push buttons, normally closed auxiliary contacts, and momentary control for reliable motor control.

Learn how to wire a two-motor power circuit with overload protection, contactors, and fuse box protection, including supply wiring, terminal connections, and relay layouts.

Design a dual-motor control circuit for Isatou motors enabling independent start and stop of each motor using fuses, terminals, start/stop buttons, contactors, and overload protection.

Design a control circuit to start two motors from one point and stop them simultaneously in overload. Use normally closed overload relay contacts in series to trip both motors.

Design a two-motor control circuit where motor two cannot start until motor one starts, using normally open auxiliary contacts and a contactor to interlock the circuit.

Design a two-motor control circuit where starting motor 1 automatically disconnects motor 2 using a normally closed auxiliary contact, demonstrated in a software simulation.

Design a two-motor control circuit under two conditions using a normally open auxiliary contact from contactor two in series with the second contact to enable continuous operation.

Learn to design a dual-motor control circuit using a double push button, normally open and normally closed contacts, and a contactor to start one motor while stopping the other.

Explore building and simulating a dual-motor control circuit that starts one motor while stopping the other, using a library-based simulation program, contactors, pushbuttons, timers, and single-phase and three-phase motor models.

Design a three-motor control circuit with motor overload protection, enabling start/stop of any motor and sequential starting: motor 2 after motor 1, motor 3 after motor 2, via auxiliary contacts.

Develop a control circuit that makes motors two and three start automatically after motor one, using normally open contactors to remove manual start/stop and enable stop via the stop button.

Learn how to reverse a three-phase induction motor by swapping two phases and applying interlock between forward and reverse contactors in power and control circuits.

Learn how to reduce components in a reversing motor control circuit using a selector switch to connect hot wire across two circuits, enabling forward, off, and reverse operations.

Design an elevator control circuit that uses a contactor and normally closed limit-switch contacts to auto stop at floors and reverse motor direction from forward to reverse using start buttons.

Explore an elevator control circuit simulation that uses forward and reverse motor rotation with a distance limit, interlocks, and limit switches to travel between floors.

Explore controlling a single phase induction motor with a capacitor start circuit, hot and neutral connections, a start/stop switch, and a contactor, sharing a control circuit with other motors.

Explore DC injection braking for a three-phase induction motor by using a rectifier and contactors, with overload protection and a variable resistor to control braking torque for precise stops.

Describe a motor braking control circuit with interlocked circuits for operation and braking, using normally closed contacts and a two-way pushbutton to energize K1 and return to normal on stop.

Design a two-motor power and control circuit in which the second motor starts after a defined delay using a timer and contactors, with auxiliary contacts managing start and stop.

Design a two-motor control circuit that starts the second motor automatically after the first, using timer relays, normally open and normally closed contacts, and interlocks for safe, sequential operation.

Analyze star and delta connections in three-phase systems, deriving line and phase voltage and current relationships using vector diagrams and 120-degree phase shifts.

Compute line and phase currents for star and delta motor starters using a 400 V ac supply, and compare voltage and current reductions between the two configurations.

Calculate active, reactive, and apparent power in three-phase star and delta connections using line voltage, line current, power factor, and P = √3 V_line I_line cos φ.

Connect a six-terminal induction motor in star or delta by pairing starts and ends (W1, W2) and wiring the power source to each start.

Explore star/delta motor control using three contactors—start, star, and delta—with a timer that switches from star to delta, using interlocked normally closed auxiliary contacts and push-button control.

Define the earthing system and its role in directing the immediate discharge of electrical energy to the earth through low resistance, protecting the system and enclosure by grounding the neutral.

The lecture outlines three earthing network types, detailing how earth bonds to supply neutral, direct earth bonding, and enclosure earth connections, with transformer earth either separate or tied to neutral.

Explain how the TT earthing system connects machine enclosures and power sources, including transformers or generators, to earth through earth resistance, delivering simple, reliable protection in industrial settings.

Explore the IT earthing system, where the neutral is not connected to earth, ensuring continuity of operation and no leakage current during insulation faults.

Explore the TN earthing system and how protective earth and neutral conductors integrate in three phase system, from protective areas to service head, ensuring earth and neutral separation.

Explore earth system components and grounding basics, including protective earth conductors and electrodes, and how soil resistivity is affected by salt, moisture, temperature, depth, and electrode count.

Learn how to select protective gear and determine conductor cross-sectional area using short-circuit current, time, and the constant K, with copper conductor, transformer, and cable examples.