Hitachi Design Engineer Interview Questions and Answers

CT current can be calculated by dividing the primary current by the turns ratio of the current transformer.

• CT current = Primary current / Turns ratio

• Primary current is the current flowing through the primary conductor

• Turns ratio is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding

Lockout is a safety procedure used to ensure that machinery or equipment is properly shut off and cannot be restarted until maintenance or servicing is completed.

• Lockout involves isolating energy sources to prevent accidental startup.

• Lockout devices like padlocks and tags are used to physically lock equipment.

• Lockout procedures must be followed to prevent accidents and injuries.

• Examples of lockout include locking out e...read more

IP65 for panel refers to the level of protection against dust and water ingress.

• IP65 rating means the panel is dust tight and protected against water jets from any direction.

• The first digit '6' indicates the level of protection against solid objects like dust.

• The second digit '5' indicates the level of protection against water ingress.

• Commonly used in outdoor or industrial applications where the panel may be exposed to...read more

TCS and Master Trip Relay are protective devices used in electrical systems to prevent damage during faults.

• TCS stands for Time Current Characteristic Relay, which operates based on the relationship between time and current to trip the circuit breaker during faults.

• Master Trip Relay is a relay that receives signals from various protective relays and initiates a trip signal to disconnect the circuit in case of a fault.

• B...read more

LSC 2A and LSC 2B are standards for lighting in commercial and industrial buildings.

• LSC 2A and LSC 2B are part of the Lighting Power Density (LPD) requirements in building codes.

• LSC 2A is for commercial buildings while LSC 2B is for industrial buildings.

• They specify the maximum allowable power consumption for lighting per unit area in a building.

• For example, LSC 2A may require a maximum LPD of 0.9 watts per square foot

REF protection is used to prevent damage to equipment from electrical faults. High impedance protection is used for sensitive equipment, while low impedance protection is used for power systems.

• REF protection is used to detect ground faults and prevent damage to equipment.

• High impedance protection is used for sensitive equipment that requires high accuracy and low fault currents.

• Low impedance protection is used for pow...read more

ANSI codes are used to identify various types of protection devices in electrical systems.

• ANSI code 50/51 is for instantaneous overcurrent protection

• ANSI code 67 is for directional power protection

• ANSI code 87 is for differential protection

• ANSI code 59 is for overvoltage protection