Authentic Exin Certification Exam CDCP Questions Answers

A UPS (uninterruptible power supply) that is categorized as VFD class is not a fit for your mission-critical data centre, because it does not provide adequate protection against voltage and frequency variations. VFD stands for Voltage and Frequency Dependent, which means that the output voltage and frequency of the UPS depend on the input voltage and frequency. VFD UPSs are also known as offline, standby, or line-interactive UPSs. They typically switch to battery power only when the input power fails or goes beyond a certain threshold. However, this switching may cause a brief interruption or a transient in the output power, which can affect the performance and reliability of the ICT equipment. Moreover, VFD UPSs do not filter or regulate the input power, which means that they pass on any voltage or frequency fluctuations, harmonics, or noise to the output power. These power quality issues can also damage or degrade the ICT equipment and the data.

For your mission-critical data centre, you need a UPS that is categorized as VFI class, which stands for Voltage and Frequency Independent. VFI UPSs are also known as online, continuous, or double-conversion UPSs. They provide a constant and clean output power that is independent of the input power. VFI UPSs convert the input AC power to DC power, and then convert it back to AC power with the desired voltage and frequency. This double conversion process isolates the output power from the input power, and eliminates any power quality issues. VFI UPSs also have zero switching time, which means that they do not cause any interruption or transient in the output power when switching to battery power. VFI UPSs are designed to protect the ICT equipment and the data from any adverse effects of voltage and frequency variations, and to ensure the highest level of availability and reliability.

References:

1: CDCP Preparation Guide, page 17, section 2.3.1 2: Understanding UPS Classification: Fuji Electric’s Technical Guide3, page 1, section 1 4: Uninterruptible Power Supplies Key Product Criteria5, page 1, section 1 6: UPS Function: Reduced Input Voltage for VFDs - KEB7, page 1, section 1

According to the CDCP Preparation Guide1, risk can be defined as the product of impact and probability. Impact is the measure of the negative consequences or losses that may result from a risk event, such as downtime, data loss, or damage to the data centre. Probability is the measure of the likelihood or frequency of a risk event occurring, based on historical data, expert judgment, or statistical analysis. By multiplying impact and probability, risk can be quantified and compared, which helps in prioritizing and mitigating the risks. For example, a risk event that has a high impact but a low probability may have the same risk level as a risk event that has a low impact but a high probability.

References:

1: CDCP Preparation Guide, page 25, section 2.5.1 2: Data center risk assessment: A decision-making tool3, page 1, section 1 4: Accounting for Risk in Your Data Center Design/Build Strategy5, page 1, section 1 6: A Novel Framework for Data Center Risk Assessment7, page 1, section 1

Shielded twisted pair cables (STP) are Ethernet cables that feature additional protection against electromagnetic interference from external sources, such as radio waves, microwaves, or other network cables. This is achieved by wrapping each pair of wires with a conductive shield, usually made of foil or braided wire, and then enclosing the entire cable with another shield layer. However, this shielding is not effective against low frequency electromagnetic fields (EMF) from power cables, which can induce currents and voltages in the network cables and cause signal distortion or data loss. Low frequency EMF can only be reduced by increasing the distance between the power and network cables, or by using a tre-foil cable arrangement, which is a special configuration of three power cables twisted together to cancel out the magnetic fields they generate.

References: STP Cable: Your Shield Against Network Disturbances; What is Shielded Twisted Pair Cable? - Advantages, Disadvantages; Shielded vs. Unshielded Cables: What’s the Difference? - Cable Matters.