Vehicle Intelligent Earthing confirmation system

 

Introduction

 

The loading and unloading of tankers with flammable and combustible products, presents one of the most serious fire and explosion risks for site operations. For sparking to occur in tanker product transfer operations, other conductive objects must come in close proximity with charge container of tanker. The charges on tanker attract opposite charges to the surface of the object and rapidly create an electric field between their respective surfaces. It is the strength of this electric field that causes the breakdown of the air between container and the object. When air is broken down a conductive path for the excess charges to rapidly discharge themselves is created, leading to static spark discharge. If a combustible atmosphere is present in this space, ignition of the atmosphere is very probable.

 

Standards governing the static control of tanker product transfers

 

The standards namely, NFPA 77, API RP 2003 and IEC 60079-32 state that earthing of tankers should be the first procedure to be carried out in the transfer process. Earthing effectively creates an electrical circuit that connects tanker to the earth and this connection prevents static charges accumulating on the tanker’s container. The electrical resistance of this circuit from the tanker to earthing point which is in contact with the earth is a key performance indicator of the entire grounding circuit’s capacity to provide a secure and safe product transfer operation. NFPA 77 and API RP 2003 state the resistance in a healthy metal circuit should never exceed 10 ohms, therefore the entire circuit between the truck and the grounding point should be measured and be equal to, or less than 10 ohms.

 

ECR Plus

 

Excel has indigenously developed a comprehensive, reliable and proven solution for static charge control during the tanker product transfer operations i.e. ECR Plus.

The ECR Plus continuously monitors the resistance between the tanker and the earthing point connection. The system is interlocked with the transfer system to shutdown the product transfer operation if the resistance exceeds 10 ohms. It also recognizes when it is not connected to the chasis/ metal tank of the tanker.  This ensures that the connection to the mudguard or the wheel nut by the operator would not allow the transfer operation and the prevents the associated risk of accumulation of static charge on the tanker.

 

Principle of operation

 

ECR plus is connected to the bolted connection to the earthing point of the local earthing grid and the tanker chasis/metal body using the special tungsten carbide tip clamp to ensure proper contact of the tanker metal part to the clamp. After ensuring the connections are secured properly, ECR Plus is switched on to perform the following prerequisite steps:

Step 1 – Residual Static charge dissipation: ECR Plus dissipates static charge from the tanker body to earth, to ensure that there is no static charge accumulation on the tanker prior to the pump operation for transfer of fluids.

Step 2 – Road Tanker recognition: ECR plus analyses the capacitance of the tanker and if the capacitance measured is in the normal range for tankers, the earthing system will recognize that it has made proper connection to the tanker. This eliminates the risk of connecting the clamp to other parts of the tanker which are not suitable for dissipation of static charge.

Step 3 – Static ground verification: ECR Plus checks and ensures the earthing connection. However, proper earthing is a critical for transfer of static charges from road tanker to earth and it is assumed that the buried earth electrode or earth grid to which the system is connected has been independently verified for having low resistance connection to earth. The site operator shall ensure that the earth resistance tests are periodically conducted to ensure earth connections do not deteriorate due to changes in soil resistivity, composition and corrosion of earth electrode.

Step 4 – Continuous ground loop monitoring: ECR Plus continuously monitors the earth loop resistance so that, the loop resistance does not exceed 8 ohms. As soon as the loop resistance exceeds 8 ohms, the interlocking contact for pump control prevents the pump operation to stop the transfer of fluid.

ECR plus ensures that the prerequisites are fulfilled to allow loading/ unloading operation through the above four steps. When the above prerequisites are fulfilled, ECR plus goes healthy and energizes the changeover relay for operation of pump or the interlocked equipment used for flow of fluid in or out of tanker.

 

Features

 

  • Housed in flame proof/ weather proof enclosure to suit hazardous area application.
  • Intrinsically safe relay operation.
  • ATEX and CE certified equipment.
  • One or two stainless steel earthing clamp with/ without tungsten carbide teeth for clamping to the tanker.
  • Two changeover potential free relay output contacts.

 

Advantages 

                                                                         

  • Easy installation: Supplied as complete assembled unit and can be easily installed on wall or steel frame structure.
  • Ease of operation. When the system is made ready by clamping to the tanker and fixing the earth connection; red indication lamp glows if earth connection is open or earth resistance is more than 8 ohms or tanker is not identified and green lamp glows when the pre-requisites are fulfilled for healthy condition allowing the pump operation for loading/ unloading of fluids.
  • Continuous monitoring of loop earth resistance and tanker verification ensures that human errors during the earth connection and tanker connection are prevented.

 

Technical Specification 

 

Rated Power supply        :               230VAC or 110VAC, – 10%/ +15%, 45-65 Hz (optional 24V AC/DC)

Internal Protection          :               High speed glass fuses for short circuit protection

Inputs                                   :               1) True or verified earthing at loading/ unloading area

2) Clamp connection from Tanker

 

Setting Range                    :               Earth Loop resistance 0 to 10 Ohms adjustable through external

display console at factory on demand.

 

 

Permissible circuit values

ignition protection class :               EX IIC 2 GD d e ia T6

 

Temperature class           :               T6 (85 degC)

 

Output relay details        :               Two change over contacts rating of 250V, 5 A (resistive load)

 

Cable entry points           :               Three/ four at the bottom of enclosure

Cable type                          :               Two single core or two core single cable of 5m

(Option in straight and spiral)

 

Clamp design                     :               SS 304 crocodile type / tungsten carbide (optional)

 

Weight                                 :               6.5kg (without clamp)

 

General FLP Enclosure Certification 

 

  • Type of Protection                      :               CIMFR / CCOE for Intrinsic safety (Ex-i)
  • Flame proof (Explosion proof):               Ex-d
  • Area Classification                     :               Zone 1 & 2
  • Gas Groups                                  :               IIA/IIB, T6
  • IP Protection                               :               IP 65/ IP 66
  • Apparatus Standard                  :               For Ex-d- IS/IEC 60079-1: 2007, IS/ IEC 60529-1: 2001 (IP-66)
  • Material                                       :               Cast Aluminum Alloy LM – 6
  • Temperature Class                    :               T6 (85 deg.C)