Electrical Power Equipment Maintenance and Testing Flashcards

Practice flashcards covering maintenance, testing, sizing, and standards for medium-voltage and low-voltage switchgear, circuit breakers, and battery systems.

How often should maintenance tests be performed on breaker closing mechanisms?

About every $3$ years.

What specific tool is designed to test MV breakers with a common operating mechanism and a single break per phase?

The Megger Programma EGIL breaker analyzer.

What is the DualGround testing method for HV circuit breaker timing called?

Dynamic capacitance measurement (DCM).

Why are safety grounds placed on both sides of a breaker during the DCM test?

To protect test personnel from unwanted induced currents and voltages from adjacent energized lines.

What circuit type do HV circuit breakers exhibit in an open state during a DCM test?

A capacitive circuit.

What are the two main types of control voltages used for MV switchgear?

(1) DC control and (2) AC control.

What is the most important requirement of a control power source in switchgear?

It must provide tripping power to circuit breakers.

What are the standard nominal DC control voltages listed in NEMA Table 7.9?

$24$, $48$, $125$, and $250\text{ V}$.

When is a $48\text{ V}$ battery recommended for MV switchgear?

For tripping only (when higher voltages are not available).

What are the two types of capacitor trip devices?

Nonautocharge and autocharge.

How long does a nonautocharge capacitor trip device retain its charge after the AC supply is lost?

About $30\text{ s}$.

What are the three AC methods of tripping used in switchgear?

AC shunt trip, circuit opening relays, and tripping transformers.

Why is a DC battery preferred for breaker closing power?

It is independent of voltage conditions on the power system.

What is the capacity of a battery usually expressed in?

Ampere-hours (product of discharge current and time in hours).

What is the expected life of a lead-calcium battery in switchgear applications?

About $25$ years.

What is another name for a Valve-regulated lead-acid (VRLA) battery?

Maintenance-free battery.

What is the practical float voltage (VPC) for Nickel-cadmium batteries?

$1.4\text{--}1.42\text{ VPC}$.

What is the practical float voltage (VPC) for Lead-calcium batteries?

$2.17\text{--}2.25\text{ VPC}$.

How frequently should battery inspections (checking float voltage and electrolyte levels) be performed?

At least once a month (more frequently/weekly depending on service).

Which IEEE standard provides practices for the maintenance and testing of vented lead-acid batteries?

IEEE standard 450-2002.

At what point of its service life should an annual performance test be conducted on a battery?

When it has reached $85$% of its service life.

What defines "degradation" of a battery capacity?

If capacity falls more than $10$% from the previous test or reaches $90$% of the manufacturer's rating.

What is the normal connection resistance range for a large battery?

Less than $10\text{ }\mu\Omega$.

What percent change in connection resistance from the baseline should initiate corrective action?

A $20$% change.

What solution should be used to clean acid spillage on a battery exterior?

A cloth dampened in baking soda solution.

At what voltage level is low-voltage switchgear typically rated?

$600\text{ V}$ alternating current (AC) and below.

What are the three types of low-voltage circuit breakers?

(1) Molded-case circuit breakers (MCCBs), (2) insulated-case circuit breakers, and (3) fixed or draw-out power circuit breakers.

What is the primary application for magnetic-trip-only MCCBs?

Motor circuit protection (short-circuit protection).

What are the three components of a complete static-trip system?

(1) Primary circuit current transformers, (2) the static logic box, and (3) the tripping actuator.

Why do microprocessor trip elements utilize RMS sensing?

To avoid false tripping problems due to harmonic currents generated by nonlinear loads.

How does a current-limiting fuse differ from a noncurrent-limiting fuse?

A current-limiting fuse extinguishes the arc in a half-cycle or less, preventing the current from reaching its maximum peak value.

What term describes the condition when fault current continues to flow from remaining phases after a fuse blows?

Backfeeding.

What are the three categories of low-voltage disconnect switches?

(1) Isolating switches, (2) safety switches, and (3) interrupter switches.

What is the interrupting capability of an interrupter switch?

At least $12$ times its continuous current rating.

What is 'AIC' as applied to low-voltage circuit breakers?

Interrupting ampere capability (rated short-circuit current).

What is the maximum voltage rating for a breaker applied in a $480\text{ V}$ electrical system?

$508\text{ V}$.

What power factor is used as the cap for maximum asymmetry for low-voltage circuit breakers?

$0.15$ (or $X/R$ ratio of $6.6$).

What is the duration for a rated momentary current test in switchgear assemblies?

$10$ cycles.

According to ANSI Table 8.5, what is the total number of operations for a $1600\text{ A}$ frame power circuit breaker?

$4000$ operations.

What four actions define 'servicing' according to industry standards for breakers?

Adjusting, cleaning, lubricating, and tightening.

What is 'tracking' in the context of switchgear insulation?

An electrical discharge phenomenon caused by voltage bridging insulating members phase-to-phase or phase-to-ground.

Under what voltage is corona generally not a problem?

$600\text{ V}$ switchgear (usually occurs at $5\text{ kV}$ and higher).

What is the typical maintenance frequency for low-voltage power circuit breakers?

Annually.

What is the verified condition where a breaker fails to close contacts while a trip signal is present?

Trip-free operation.

What are the maximum primary circuit resistance values for a $3000\text{ A}$ breaker?

$20\text{ }\mu\Omega$.

What is used to clean soot and dust from arc chutes?

A pressure-regulated jet of air.

What test is used to detect absorption of moisture or thermal aging in breaker insulation?

Insulation resistance measurement (Megger).

What precaution must be taken when cleaning arc chutes containing asbestos?

Correct breathing apparatus must be worn by personnel.

What is the main cause of failure or malfunction in Molded Case Circuit Breakers (MCCBs)?

Lack of exercise of the operating mechanism.

What solution is used to remove corrosion from battery terminals?

Baking soda solution (cleaned with a brass brush).