प्राविधिक – इलेक्ट्रिकल, मेकानिकल र टेलिकम
प्राविधिक – इलेक्ट्रिकल, मेकानिकल र टेलिकम
Technical – Electrical, Mechanical & Telecom · ४,५०० प्रश्न
४,५०० प्रश्न उपलब्ध। मोड छान्नुहोस्:
इलेक्ट्रिकल र टेलिकम: प्रश्न र उत्तर
सही लागेको विकल्पमा थिच्नुहोस्। सही भए हरियो, गलत भए रातो देखिन्छ; ३ सेकेन्डपछि सही उत्तर र व्याख्या देखिन्छ।
सही: ० / ०
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In an inverse-time overcurrent relay, as the fault current increases the operating time:
सही उत्तर: क) decreases
Inverse characteristic: the larger the current (more severe the fault), the faster the relay trips.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Distance (impedance) relays are mainly used for the protection of:
सही उत्तर: घ) transmission lines
A distance relay measures V/I (impedance to the fault), which is proportional to the distance along a line, giving selective zone protection.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In an AC circuit breaker, the arc between the separating contacts is finally extinguished:
सही उत्तर: घ) at a natural current zero
AC current passes through zero every half-cycle; the breaker builds up dielectric strength faster than the restriking voltage so the arc does not restrike after a zero.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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For medium-voltage (about 11–33 kV) distribution switchgear, the circuit breakers now most widely used are:
सही उत्तर: ग) vacuum circuit breakers
Vacuum interrupters need little maintenance and have excellent arc-quenching at medium voltages; SF₆ dominates at higher transmission voltages.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Differential protection of a transformer or generator operates on the principle of:
सही उत्तर: घ) comparing the currents entering and leaving the protected zone
Under normal conditions or external faults the two currents balance; an internal fault upsets the balance and operates the relay.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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An overcurrent relay is set at 100% of its 5 A rating and fed from a 400/5 A CT. For a fault current of 4000 A, the plug setting multiplier (PSM) is:
सही उत्तर: ख) 10
Relay current = 4000 × 5/400 = 50 A; PSM = 50/(1.0 × 5) = 10.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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Series reactors (current-limiting reactors) are installed in power systems mainly to:
सही उत्तर: क) limit the short-circuit current
Their reactance adds to the fault path, limiting fault current to a level the breakers can interrupt.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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In power systems, the most frequently occurring type of fault is:
सही उत्तर: ग) the single line-to-ground fault
About 70–80% of faults on overhead lines are single line-to-ground (e.g. flashover of one insulator); symmetrical three-phase faults are the rarest.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A generator reactance is 0.1 pu on its own 10 MVA rating. On a 50 MVA base at the same voltage, its per-unit reactance is:
सही उत्तर: ख) 0.5 pu
Z_new = Z_old × (MVA_new/MVA_old) × (kV_old/kV_new)² = 0.1 × 50/10 = 0.5 pu.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
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A 10 MVA transformer has a reactance of 10% (0.1 pu). Ignoring source impedance, the fault level for a three-phase fault at its terminals is:
सही उत्तर: क) 100 MVA
Short-circuit MVA = base MVA/Z_pu = 10/0.1 = 100 MVA.
💬 टिप्पणी / गल्ती रिपोर्ट (०)
यी अभ्यास प्रश्न हुन्, आधिकारिक प्रश्न होइनन्। पाठ्यक्रम, विज्ञापन र नतिजाका लागि सम्बन्धित निकायको आधिकारिक वेबसाइट हेर्नुहोस्। उत्तरमा गल्ती भेटे प्रश्नमुनिको "टिप्पणी / गल्ती रिपोर्ट" मा लेख्नुहोस्।
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