The indicating and metering instruments used in substations are

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Option D: All of above

Explanation & Concepts:
Substations require a comprehensive suite of instrumentation to monitor, control, and protect the electrical network. These include indicating instruments for real-time monitoring of voltage and current, and integrating meters to track cumulative energy consumption and billing metrics.

Working Principle: Indicating instruments utilize electromagnetic or electrodynamic deflection to provide instantaneous readings of quantities like voltage, current, and power factor. Integrating instruments, such as kWh meters, utilize induction-type mechanisms or solid-state digital processors to sum the energy consumed over a period ($E = \int P dt$). These devices are interfaced with primary power lines using potential transformers (PT) and current transformers (CT) for safe and accurate isolation and measurement.

Key Formulas: $E = \int_{0}^{t} P(t) dt$ — Energy measurement principle; $P_{3\phi} = \sqrt{3} V_L I_L \cos \phi$ — Real power monitored by meters

Key Points: Indicating instruments provide instantaneous values to operators.; Integrating instruments track energy usage over specific time intervals.; Instrument Transformers (CT and PT) are essential for stepping down high values to levels suitable for standard metering devices.; Power Factor meters help in monitoring reactive power compensation needs.

Advantages: Provides real-time visibility into substation health.; Enables accurate billing and demand management.; Facilitates diagnostic analysis during fault conditions.

Disadvantages: Requires regular calibration to maintain accuracy.; Complexity increases with the addition of digital communication modules.

Applications: Grid monitoring and control centers.; Energy auditing and billing for industrial loads.; Substation automation and fault recording.

Additional Info: Standard substation meters usually operate at a secondary voltage of 110V and a current of 1A or 5A, derived from PTs and CTs respectively.. Option A focuses on instantaneous values, while Option C focuses on cumulative energy values; both are essential.

Answer: D is correct — Substations require both instantaneous indicating instruments and cumulative integrating meters to ensure complete operational data collection.

Exam Tip: Always remember that in power systems, metering is classified into indicating (current, voltage), integrating (energy), and recording (charts/data logs).

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Option A: Ammeters and voltmeters

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Option B: Power factor meters

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Option C: kWh, KVARh and kVAh meters

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