Nowadays most of the solar power plants use power and electronic equipments. The performance of these equipments & safety of personnel vastly depend on the earthing practices we adopt. As all these equipments are assembled together their performance depends on their system & equipment grounding.
Types of Earthing related to Power Earthing System Design & Electronic Earthing System Design:
In this type of earthing both Power Earthing System Design (among different voltage levels) and Electronic Earthing System Design are independent & there is no intended physical interconnection. If there is any unintended interconnection then it becomes a safety hazard to Personnel & affects the performance of Electronic Equipments. The Equipment Grounding Conductor (EGC) Cross Section shall be designed for respective fault levels.
Here both Power Earthing System Design and Electronic Earthing System Design are connected to the common Earth Electrode. The common earth electrode is designed as per max fault level contributing among both (whichever is higher) the Power Earthing System Design and Electronic Earthing System Design.
Integrated or Interconnected Earthing
Both Power Earthing System Design and Electronic Earthing System Design for respective Earth Electrodes such as Earth mat, Horizontal Conductor & Vertical Earth Electrodes are designed for Earth Fault Current Levels. The designed respective Earth Electrodes are interconnected/integrated with the bonding conductor. The bonding conductor shall be of the maximum conductor cross-section among both the Power Earthing System Design and Electronic Earthing System Design.
The EGC of Power Equipments & Electronic Equipments shall be the same. The EGC shall be routed from Power equipment to Electronic equipment. This common EGC shall be connected to a common earth electrode designed for maximum fault level current. This earthing is very rare to implement in Industry because of Personal Safety Hazard & operation of equipment would get affected if there is a breakage of EGC. So, utmost care shall be taken for EGC redundancy.
*Note that Manufacturer recommendations need to be taken regarding Electronic Earthing as the warranty terms
might get affected if the Earthing requirements mentioned in the instruction manual are not met. If the manufacturer practices were contradicting with the standards then the same shall be brought to Manf’s notice, discussed & resolved.
*Note that the terminology Earthing & Grounding will be used interchangeably.The choice of Interconnected or Isolated grounding depends on the perspective of Power Oriented Engineers & Signal Oriented Engineers.
The Power Oriented Engineers were worried of Safety due to the following two reasons:
Results in Transferred Voltages if the Grounding Systems are not isolated completely such as Grounding the Control/Communication Cable conductor screen at one end of the cable termination, Lightning Surges cause transferred voltages if the Earthing Conductors or via any other means such as pipes, cable conductor screens enters from one Grounding System to the other grounding system vicinity.
This method of Earthing in past standards was termed as ‘clean’ electronic ground. It was assumed trouble-free most of the time as it cannot pick up the stray currents from Power System Grounding but it was not true, the same shall be discussed in “The Signal Oriented Engineers misconception regarding Isolated Earthing”.
The ‘clean’ electronic ground situation becomes positively dangerous when there is a surge due to lightning or faults, because the cables/conductors interconnecting the power grounding system & Electronic Equipment or other metal parts or building structures or flooring in its vicinity can all assume a high potential due to rise in potential continuously or intermittently, during lightning surges and faults.
Clean ground which does not develop these high potentials remains at true ground potential causes a potential difference between Electronic Equipment & the High Potential developed vicinities.
This situation gives rise to inherently unsafe situations for personnel due to unsafe touch potentials and for the equipment (potential stress on the electronic items) connected to the ‘clean ground’.
Another problem with an isolated ground is that the ground resistance of a system, which uses one or two electrodes, is much higher than the interconnected ground and common ground.
The Signal Oriented Engineers misconception regarding Isolated Earthing
It’s a misconception that isolated earthing avoids interference as it cannot pick up the stray currents which is not true if both the Earthing Systems – Power & Electronic are not isolated completely in all respects.As per revised IEEE 1100 standard, when sensitive Electronic Equipments Earthing were made isolated with Power System Earthing (Interconnected earthing) causes interference because when any conductor (Cable, EGC,..) originating from / terminated to – Electronic Equipments and the conductor path was through two different vicinities with different reference grounds causing different Earth Potential Rise may lead to circulating currents through the conductor medium causing interference i.e., unwanted noise in the Electronics Circuits.
Integrated or interconnected Earthing
The Earthing System design of Power & Electronic Equipments shall be designed separately as per their respective fault levels & parameters influencing their system design.The technical issues of Isolated Earthing were overcome by the Integrated or Interconnected Earthing but the Bonding Conductor selected shall be of the maximum conductor cross-section derived among both the Power Earthing System Design and Electronic Earthing System Design.Utmost Care on redundancy & quality of Bonding Conductors shall be taken; if the bonded conductors fail to interconnect both the Earthing System Design then it would be a safety hazard.
Both the Power Earthing System Design and Electronic Earthing System Design shall have a common Earth electrode & need to be designed for maximum fault level among both.
Another problem with a common ground is that the ground resistance of a system, which uses one or two electrodes, is much higher than the interconnected ground.
The EGC of Power Equipments & Electronic Equipments shall be the same. The EGC shall be routed from Power equipment to Electronic equipment. This common EGC shall be connected to a common earth electrode designed for maximum fault level current.
This earthing is very rare to implement in Industry because of Personal Safety Hazard & operation of equipment would get affected if there is a breakage of EGC. So, Utmost care shall be taken for EGC redundancy.
If the Earthing System Designs were not isolated in all respects both physically and electrically, isolated earthing practice will be an hazard to operating personnel and operation of equipments.
Thus Interconnected Earthing is the recommended Earthing practice among all the discussed Earthing Practices.
Kiran Kumar Alla
Senior Electrical System Design Engineer at Punj Lloyd
Kiran is a solar professional passionate about Solar PV System Design & Engineering with an industry experience of 4 years and currently
working in Punj Lloyd Surya Urja Ltd as a Senior Engineer.