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BISCI - DCDC > Chapter 10: Electrical Systems > Flashcards

Chapter 10: Electrical Systems Flashcards

1
Q

Bonding

A

The permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safety any current likely to be imposed.

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2
Q

Grounding

A

Making a conducting connection between an electrical circuit or equipment and the earth or to some conducting body that services in place of earth.

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3
Q

Failure Mode

A

A system state resulting from an unanticipated system outage and typically an automatic system response to that failure.

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4
Q

Grounding Electrode System

A

Network of electrically connected grounding electrodes used to achieve a low-impedance path to ground (earth).

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5
Q

Nominal Voltage

A

The voltage at which the ITE is expected to operate under normal conditions of normal operation.

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6
Q

NOx

A

A generic term for the mono-nitrogen oxides; NO and NO2 (nitric oxide and nitrogen dioxide).

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7
Q

PDU

A

Power Deployment Unit. This is a floor- or rack-mounted enclosure for distributing branch circuit electrical power via cables, either overhead or under the access floor, to multiple racks of enclosures of ITE.

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8
Q

Power Strip

A

A device mounted onto or within ITE rack or enclosure, supplied by a single branch circuit, and containing power receptacles into which multiple IT devices can be plugged. A power strip is identified within IEEE 1100 as a power outlet unit or POU.

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9
Q

RPP

A

Remote Power Panel. A power distribution cabinet downstream from a PDU or UPS, typically containing circuits and breakers, without a transformer, located near the load.

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10
Q

Switchgear

A

An electrical enclosure, typically having both front and rear access, containing overcurrent protective devices, such as fuses and circuit breakers, used to isolate electrical equipment.

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11
Q

Short Circuit

A

A low resistance connection between the two conductors supplying electrical power to any circuit that may result in excessive current flow in the power sources through the “short,” and may even cause the power source to be destroyed.

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12
Q

Which class shall be any data center that doesn’t meet the minimum requirements of Class F1?

A

Class F0

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13
Q

Whom should you consult if electrical equipment need to be used above the specified altitude range?

A

Consult with the equipment manufacturer concerning operational limits and restrictions.

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14
Q

Which classes require the reduction single points of failure within the electrical systems to the greatest extent possible?

A

Class F3 & F4

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15
Q

When describing levels of redundancy, what does the term “N” mean?

A

N = Need or Baseline Requirement

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16
Q

This type of redundancy provides one additional unit, module, path, or system in addition to the minimum required to satisfy the base requirement. The failure or maintenance of any single unit, module, or path will not disrupt operations.

A

N+1

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17
Q

What does the term “N+2 redundancy” mean?

A

This type of redundancy provides two additional units, modules, paths, or systems in addition to the minimum required to satisfy the base requirement. The failure or maintenance of any two single units, modules, or paths will not disrupt operations.

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18
Q

Explain 2N redundancy

A

2N redundancy provides two complete units, modules, paths, or systems for every one required to satisfy the base requirement. 2N is also referred to as “dual-path topology.” Failure or maintenance of one entire unit, module, path, or system will not disrupt operations.

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19
Q

In what type of system is a multi-N redundancy typically used?

A

A multi-N system topology is used primarily in fault tolerant or large-scale power systems where more than two large systems are employed together. In such a system topology, the critical load connection at the PDU or the branch circuiting level is the primary means of achieving the redundancy and class of the system.

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20
Q

Define the term “capacity”.

A

The kW required to serve the load, plus the design margin and growth factors.

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21
Q

Other than redundancy, what are some factors that can affect Availability Class over the life of the data center?

A
  • Capacity
  • Expandability
  • Maintainability
  • Survivability
  • Quality
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22
Q

Classes F2 and F3 systems are very similar. In what way do they differ?

A

Class F3 systems possess the second power path.

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23
Q

List the kinds of questions asked when defining a class.

A
  • Is the load disconnected with a given outage?
  • Is the load disconnected during a given maintenance activity?
  • Is redundancy lost with a given outage?
  • Is redundancy lost with a given maintenance activity?
  • For components that are deferred from the initial construction, can they be added transparently to the existing operating loads, or is a shutdown or some form of accommodation in excess of optimum facility operation required?
  • If a system load changes on the UPS or generator, will that affect the class?
  • How long can the system run with an absence of power?
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24
Q

What class system possesses component redundancy but doesn’t have system redundancy?

A

A class F2 system

25
Q

Which class possesses redundancy and must have two independent sources of UPS power to the critical load?

A

A class F4 system

26
Q

What should be the size of utility distribution equipment?

A

The utility distribution equipment should either be sized for the ultimate load for the site or should possess the ability to add capacity later without undue disruption to ongoing operations.

27
Q

Identify one way to mitigate switching surge problems for all classes.

A

Use Surge Protective Devices (SPDs) for all classes.

28
Q

What is the range for utility services that are considered medium-voltage?

A

Medium-voltage refers to utility services that are between 1001 VAC to 35 kVAC between line conductors.

29
Q

What does a maintenance bypass do?

A

A maintenance bypass allows the UPS module(s), paralleling controls, and static switch to be totally de-energized so that maintenance can be safely performed.

30
Q

List three power strip recommendations.

A
  1. Metering may be provided on individual power strips.
  2. Power strips should not have internal surge suppression.
  3. Power strips should not be placed under the access floor.
31
Q

In terms of data center operations, explain the term “load management.”

A

Load management deals with the physical connection of critical loads to the critical power system in a manner consistent with the normal, failure, and maintenance modes of operation.

32
Q

What is the most common generator problem?

A

Failure to start

33
Q

When does an open transition occur?

A

Open transition occurs when the transfer between sources breaks before the opposite connection is made.

34
Q

For what duration are the utility and generator paralleled in closed transition?

A

In the closed transition/quick transfer the utility and generator (and consequently, the site) are paralleled for less than 100 ms to up to one minute, depending on the utility provider and designer. The paralleling time is typically the operating time of the ATS or the breaker transfer pair.

35
Q

Where are UPS output distribution switchboards located?

A

UPS output distribution switchboards are located immediately downstream of the UPS power plants and extend the PDU or data processing room levels.

36
Q

What type of switching operations needs to be used for UPS output distribution switchboards?

A

Closed-transition (make-before-break) to avoid load interruption.

37
Q

Identify a major negative outcome of operating the PDU transformer too close to its rated capacity.

A

Transformer overheating, which has two other ripple effects: (1) reduced transformer efficiency and (2) increased load on cooling equipment.

38
Q

Which types of switched are used in power systems where subcycle, high-speed source switching outside of the ITE is desirable?

A

Automatic Static Transfer Switches (ASTS)

39
Q

Which types of energy storage systems are compatible with the DC systems?

A

Renewable sources of energy and short-term energy storage systems, such as photovoltaic (PV) arrays, fuel cells, microturbines, battery systems, ultracapacitors, and flywheels.

40
Q

What does the term “power factor” mean?

A

The power factor is the ratio of the real power (kW) used to do the work and the apparent power (kVA) used to supply the circuit.

41
Q

What is the rate of failure of power supplies when one leg of dual power supplies is interrupted and then returns after some period of time?

A

The failure rate of power supplies could be as high as 5%.

42
Q

How can concurrent maintainability be achieved for power distribution between the OPS and the ITE in class F3?

A

Concurrent maintainability can be achieved through manual operational processes with multiple circuits or automated systems through the use of multiple static transfer switches.

43
Q

What is an EPO System?

A

More commonly known as an Emergency Power Off (EPO), it is a means of disconnecting the electrical supply. While not mandated by the standards, it is sometimes required by local codes.

44
Q

What is fault discrimination?

A

A system design where a fault on a circuit only results in a disconnection of the first fuse or breaker upstream instead of something more catastrophic.

45
Q

What are the three basic modes of UPS operation identified by IEC 62040-3?

A
  1. Voltage and frequency dependent (VFD)
  2. Voltage independent (VI)
  3. Voltage and frequency independent (VFI)
46
Q

List two types of UPS Systems.

A
  • Static UPS Systems
  • Rotary UPS Systems
  • Hybrid UPS Systems
  • Direct Current UPS Systems
47
Q

For a lead-acid battery, what is the rated capacity where it is considered to have reached the end of its life?

A

A lead-acid battery is considered to have reached the end of its life when it cannot deliver more than 80% of its rated capacity.

48
Q

What does the term coup de fouet mean?

A

It is the nature of a lead-acid battery to take a large dip in voltage when it is first discharged, after which it recovers to or near its normal float voltage.

49
Q

Why is it important to note when a coup de fouet occurs?

A

It can cause some systems to shut down if the DC voltage drops below a threshold.

50
Q

What is the recommended method for all bonding?

A

The use of an insulated, stranded copper grounding wire, sized as recommended, and terminated by a two-hole compression lug or exothermic weld.

51
Q

How does a mesh-BN provide electrical protection in a data center?

A

It creates equipotential ground reference for the computer room and may reduce stray high frequency signals.

52
Q

What are the typical minimum requirements for an Arc Flash Warning Label?

A

Labeling should conform to requirements of local codes, but typical minimum requirements identify:
* Voltage
* Fault current
* Flash and shock boundaries
* Incident energy levels
* Recommended minimum levels of PPE

53
Q

What is the purpose of the neutral in the 480/277 VAC and 208/120 VAC system?

A

To serve only lighting and small scale loads

54
Q

__________ is the power required by the load.

A

Capacity

55
Q

Static, rotary, hybrid, and direct currents are types of __________.

A

UPS systems

56
Q

Why is power quality monitoring (PQM) recommended for a data center?

A

Power quality monitoring (PQM) is recommended because IT systems may be sensitive to power quality, transients, harmonics, and other types of waveform disruption.

57
Q

What does IEEE 450 detail?

A

IEEE 450 details the recommended maintenance, testing, and replacement practices for vented, stationary, and lead acid batteries.

58
Q

What does IEEE 1188 include?

A

IEEE 1188 provides details for the maintenance, testing, and replacement of stationary valve-regulated lead-acid (VRLA) batteries.

59
Q

What is included in IEEE 1106?

A

IEEE 1106 provides details for the maintenance, testing, and replacement of stationary vented Ni-Cd batteries.

BISCI - DCDC (18 decks)

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