Patent ID: 6031700
Filing Date: 2000-02-29
Classification: H02H

Abstract:
A ground detector for a static grounding system, comprising:a polarity test circuit connected to AC power supply, said polarity test circuit comprising a switching switch, a test switch, a polarity indicator light and a polarity test indicator light, said polarity indicator light and said polarity test indicator light each having one end respectively connected to one common contact of said switching switch, said polarity indicator light having an opposite end connected to a metal shell of said switching switch, said polarity test indicator light having an opposite end connected to the central earth wire of a single phase three-wire system and connected to a selection contact of said test switch to lead out a single-phase three-wire reference zero potential said switching switch having a first common contact connected to said polarity indicator light and said polarity test indicator light and a second common contact connected to a second selection contact of said test switch to lead out a single-phase two-wire reference zero potential, the earth wire of the single-phase two-wire or single-phase three-wire system being detected subject to the on/off status of said polarity indicator light and said polarity test indicator light when said switching switch is operated and the metal shell of said switching switch is touched with the hand;a voltage dropping and rectifying circuit, said voltage dropping and rectifying circuit comprising a transformer and a bridge rectifier and rectifying AC power supply from said polarity test circuit into DC power supply, said bridge rectifier having a negative terminal connected to the earth bus to be tested;a grounding test circuit connected to said voltage dropping and rectifying circuit to receive DC power supply from it, said grounding test circuit comprising a photoelectric means and a relay, said photo electric means having a non-inverter terminal and an inverter terminal respectively connected to the positive terminal of said bridge rectifier and the earth wire of the single-phase two-wire or single-phase three-wire system being connected to the common contact of said test switch, a positive output terminal connected to the positive terminal of said bridle rectifier and the common contact of said relay, and a negative output terminal connected to the negative terminal of said bridge rectifier through a coil of said relay, enabling the potential at the negative terminal of said bridge rectifier to be compared with the potential at the earth wire of AC power supply, so as to determine the grounding condition of the grounding bus which is connected to said bridge rectifier, and to let said relay be energized or not energized subject to the grounding condition of the grounding bus detected, causing the common contact of said relay to output or not to output an alarm driving signal; andan alarm device connected to the normal close contact of said relay and the negative terminal of said bridge rectifier, and controlled by said relay to output an alarm signal when the grounding bus which is connected to said bridge rectifier is not positively connected to earth.