Transformer ratios of 400:1 are typically used in ______ transformers, depending on installation and equipment needs.

Transformer ratios of 400:1 are typically used in ______ transformers, depending on installation and equipment needs.

• A. Instrument
• B. Potential
• C. Current
• D. Distribution

Answer: (A)

The key idea is that instrument transformers are designed to scale down high electrical quantities for metering and protection equipment. A 400:1 ratio means the secondary signal is 1/400 of the primary, so a high line voltage or current is reduced to a safe, standard level that meters or relays can handle. This kind of large step-down is typical for measurement devices because you want to feed inputs that are within their precise, low-range ratings while keeping electrical isolation from the high-power circuit. That’s why instrument transformers are the correct category here: they encompass both current and voltage types and are selected to match the installation and the input requirements of the protective relays and meters. Distribution transformers aren’t focused on measurement scaling, and while current or potential transformers exist, the broad, correct grouping for this ratio is instrument transformers.

The key idea is that instrument transformers are designed to scale down high electrical quantities for metering and protection equipment. A 400:1 ratio means the secondary signal is 1/400 of the primary, so a high line voltage or current is reduced to a safe, standard level that meters or relays can handle. This kind of large step-down is typical for measurement devices because you want to feed inputs that are within their precise, low-range ratings while keeping electrical isolation from the high-power circuit. That’s why instrument transformers are the correct category here: they encompass both current and voltage types and are selected to match the installation and the input requirements of the protective relays and meters. Distribution transformers aren’t focused on measurement scaling, and while current or potential transformers exist, the broad, correct grouping for this ratio is instrument transformers.