Unsa ang mga abilidad sa paggamit og common grounding system sa power distribution, asa kini ang mga precaution nga dapat buhaton?

Unsa ang Common Grounding?

Ang common grounding nagrefer sa praktisahan diin ang functional (working) grounding, equipment protective grounding, ug lightning protection grounding sa usa ka sistema mag-share og usa ka grounding electrode system. O kini maaari usab nang mulehok nga ang mga grounding conductors gikan sa daghang elektrikal nga devices gitugotan nga makonekta sama ug gilink sa usa o daghang common grounding electrodes.

1. Mga Advantages sa Common Grounding

• Mas simple nga sistema uban sa mas kaayo nga grounding conductors, mas sayon ang maintenance ug inspeksyon.

• Ang equivalent grounding resistance sa daghang grounding electrodes nga gitugotan nga makonekta sa parallel mas bata kaysa total resistance sa separate, independent grounding systems. Kon ang building’s structural steel o rebar gigamit isip common grounding electrode—tungod sa iyang inherent nga low resistance—mas prominent pa ang benefits sa common grounding.

• Enhanced reliability: kon usa ka grounding electrode moguba, ang uban pa makapag-compensate.

• Gihatag ang mas kaayo nga grounding electrodes, pagbawas sa installation ug material costs.

• Kon may insulation failure nga nagresulta og phase-to-chassis short circuit, ang larger fault current mogulo, sigurado nga ang protective devices molihok rapido. Kini usab nagreduce sa touch voltage kon ang personnel mogcontact sa faulty equipment.

• Pagbawas sa hazards gikan sa lightning overvoltages.

Teoretikal, aron maprevent ang lightning-induced back-flashover, ang lightning protection grounding dapat gitugotan nga safe distance gikan sa building structures, electrical equipment, ug ang ilang grounding systems. Apan, sa tunay nga mundo, kasagaran dili kini praktikal. Ang buildings adunay daghang incoming utility lines (power, data, water, etc.) na spread giwide areas. Lahi-lahi kon ang reinforced concrete structural rebars gigamit isip concealed lightning protection conductors, dili na mahimong electrically isolate ang lightning protection system gikan sa building piping, equipment enclosures, o power system grounding.

Sa mga kaso niini, gi-recommend ang common grounding—gitugotan nga ang transformer neutral, tanang functional ug protective grounds sa electrical equipment, ug ang lightning protection system gitugotan nga ma-link sa sama nga grounding electrode network. Pwede usab tibuok ang high-rise buildings, integrating electrical grounding sa lightning protection system effectively nagform og Faraday cage gamit ang building’s internal steel framework. Tanang internal electrical equipment ug conductors nga bonded sa kahon mahimong protektahan gikan sa lightning-induced potential differences ug back-flashover.

Dili lang feasible apan advantageous usab ang common grounding para sa multiple systems kon gigamit ang building’s metallic structure para sa grounding, provided ang overall grounding resistance maintained below 1 Ω.

2. Key Considerations for Common Grounding

Nature of grounding currents:
Ang risk associated sa ground potential rise (GPR) depende sa magnitude, duration, ug frequency sa grounding currents. Pwede maoy lightning arresters o rods magcarry og very high currents sa panahon sa strike, apan ang mga event niini brief ug infrequent—so ang resulting GPR poses limited risk.

Apan, ang common grounding resistance kinahanglan satisfy ang most stringent requirement sa tanang connected systems, ideally ≤1 Ω.

Sa low-voltage distribution systems uban solidly grounded neutrals, ang common grounding electrode maaari magcarry og continuous leakage currents gikan sa tanang connected loads, forming circulating ground currents. Kon ang grounding resistance drifts above safe limits, mahimo nang magdala og panganak sa both equipment ug personnel.

Bisan pa, tungod sa widespread use sa computers ug sensitive electronic equipment, required gyud ang filter grounding. Large line-to-ground EMI/RFI filters introduce significant capacitive leakage currents to earth, which also contribute sa total ground current.

Impact of ground potential rise on connected equipment:
Tan-awon ang indoor compact substation unit isip example. Traditionally, ang transformer neutral, metal enclosure, ug load equipment chassis gitugotan nga ma-link sa common ground. Sa wala pa, ang lightning arresters kasagaran gihatagan og separate ground aron maprevent ang dangerous potential rise sa panahon sa discharge.

Apan, kon ang load device mogdevelop og insulation fault ug leaks current, ang entire fault loop current mogulo pina sa common grounding electrode, raising the local ground potential—and consequently, ang enclosure voltage sa switchgear. Kon ang maintenance personnel mogopen sa cabinet door sa sulod niining kondisyon, mahimo sila mobati og electric shock. Nangyari na ang mga incidents niini repeatedly.

Tungod kay resulta, ang modern practice kasagaran isolated ang functional grounding (e.g., transformer neutral) gikan sa protective ug lightning grounding sa indoor substations—even though this increases installation complexity.

3. Relevant Standards and Regulations (China)

• Sumala sa kasamtangan nga Chinese power industry standards:

• Para sa Class B electrical installations, kon ang supplying distribution transformer dili located within a building containing Class B equipment, ug ang iyang high-voltage side operates in an ungrounded, Petersen coil (arc-suppression coil)-grounded, o high-resistance grounded system, then ang low-voltage system’s working ground may share the same grounding electrode as the transformer’s protective ground, provided ang grounding resistance satisfies R ≤ 50/I (Ω) ug R ≤ 4 Ω.

• Para sa Class A electrical installations operating in effectively grounded systems, ang transformer’s working ground must be located outside the protective grounding grid—i.e., common grounding is not permitted.

• Kon ang distribution transformer installed inside a building with Class B electrical installations, ug ang iyang high-voltage side uses low-resistance grounding, then ang low-voltage working ground may share the protective ground if:

• Grounding resistance meets R ≤ 2000/I (Ω), ug

• The building implements a main equipotential bonding (MEB) system.

• Additionally, for systems above 1 kV classified as large grounding short-circuit current systems, common grounding is permissible if rapid fault clearance is ensured, but the grounding resistance must be < 1 Ω.

• Protective grounding of distribution transformers in Class A installations may share the same grounding electrode as the associated lightning arrester grounding.

4. Conclusion

Practical experience shows that in public low-voltage distribution systems, where complete separation of grounding systems is often unachievable, common grounding—combining working, protective, and lightning grounding—is safer, more economical, simpler to install, and easier to maintain.

To mitigate potential risks of common grounding, engineers should:

• Fully utilize the building’s structural steel as a natural grounding electrode,

• Maintain total grounding resistance below 1 Ω, and

• Implement comprehensive equipotential bonding throughout the facility.

These measures effectively minimize hazards and ensure safe, reliable operation of modern electrical installations.