SACA Electrical Control Systems 3

Question 1

What is 'power factor' in AC electrical systems and why is low power factor a problem in industrial facilities?

Accepted Answer

Power factor is the ratio of real power to apparent power; low power factor means more current is drawn for the same useful work, increasing distribution losses and utility demand charges

Answer

Power factor is the efficiency of a motor at full load; low power factor reduces motor speed

Answer

Power factor measures voltage harmonic distortion; low power factor causes equipment overheating

Answer

Power factor is the ratio of input to output watts in a transformer; low power factor indicates poor insulation

Question 2

What is the purpose of a 'ground fault circuit interrupter' (GFCI) in industrial electrical systems?

Accepted Answer

To detect small leakage currents flowing to ground and quickly disconnect power to prevent electrocution

Answer

To protect high-voltage equipment from over-current faults

Answer

To provide surge suppression for sensitive PLC input cards

Answer

To balance three-phase current loads across distribution panels

Question 3

In industrial panel wiring, what is the standard color convention for DC control wiring in North America?

Accepted Answer

Red = positive (+), Black = negative (−), Green = ground

Answer

Blue = positive (+), White = negative (−), Green = ground

Answer

Red = positive (+), White = negative (−), Green = ground

Answer

Black = positive (+), White = negative (−), Green = ground

Question 4

What is the function of an 'autotransformer' starter for large induction motors?

Accepted Answer

It uses transformer taps to apply a fraction of line voltage during starting, then switches to full voltage at running speed

Answer

It continuously varies voltage from zero to full to provide smooth acceleration

Answer

It converts single-phase supply to three-phase for motor operation

Answer

It provides power factor correction during motor starting transients

Question 5

What is 'arc flash' hazard in electrical switchgear, and what does an 'arc flash study' determine?

Accepted Answer

The explosive release of energy from an electrical arc fault, causing burns and blast injury; the study determines the incident energy and required PPE category for each panel

Answer

The risk of motor windings burning during a locked-rotor condition

Answer

The risk of static discharge igniting flammable vapors near electrical equipment

Answer

Corrosion of copper bus bars from acid vapors in chemical plants

Question 6

What does 'lockout/tagout' (LOTO) procedure require before performing electrical maintenance on industrial control panels?

Accepted Answer

Isolating all energy sources, applying lockout devices, and verifying the equipment is de-energized before any maintenance work

Answer

Verifying that the emergency stop button is functional before opening the panel

Answer

Notifying the plant manager and waiting 10 minutes before opening energized panels

Answer

Wearing arc-rated PPE (category 2 or higher) while working on energized circuits