Hazardous Locations

Problem:
Electrical equipment, such as motor operated valves, on a cathodically protected structure requires safety grounding according to the electrical codes, however a direct bond will cause a short-circuit on the CP system. Likewise, tanks with electrical equipment can be affected by the bond to ground.

Solution:
Using a DEI product certified for use in a safety grounding conductor is an authorized method of providing DC isolation and simultaneous AC grounding for motors and other equipment. In the case of a valve motor, this eliminates the need for insulated joints on either side. Instead, the motor is grounded via the DEI isolation device. Certified (listed) products are needed for this application, to comply with electrical codes. See the schematic of a sample installation.

To implement an equipment/tank isolation system, the following issues need to be examined to determine product selection and ratings:
1. The maximum DC Voltage present between the structure and ground
2. Whether induced AC voltage is present at the site
3. Examine AC fault current exposure
4. Is this site classified as a hazardous Location?
5. Install the device in series in the grounding conductor, and determine that there is not an electrical bypass around the device.

See Application Note #2 for a full review of this application.

Problem:
Gradient control mats are installed around above ground pipeline structures to protect workers from potentially hazardous voltages that can be present on cathodically protected pipelines. Pipeline voltages can result from the following conditions:
• Induced AC voltage
• An AC fault in improperly grounded electrical equipment
• A lightning strike directly to or adjacent to the pipeline

The effectiveness of a gradient control mat is determined by the step potential and the touch potential that it allows for the voltage sources described. Unfortunately, no known manufacturer has provided any technical data on the effectiveness of their mat in limiting step and touch potentials. Additionally, single conductor mats such as the spiral configuration type, have been found completely ineffective in limiting step and touch potentials from lightning to safe levels.

Solution:
DEI offers the engineered Gradient Control Mat (GCM) to address lightning and AC fault current conditions, backed by analysis from experts in lightning protection and with a full review by Correng Consulting of the cathodic protection guidelines of this mat design. Step and touch potentials are now limited with the DEI grid-type mat, in a much lower cost design. DEI also recommends decoupling gradient control mats to improve CP on the pipeline, and offers the affordable Solid-State Decoupler (SSD) line for use in conjunction with the Gradient Control Mat.

A decoupling device such as the SSD is recommended for use in conjunction with the gradient control mat as it allows for several distinct advantages including:
• The galvanic potential of the mat material becomes irrelevant
• Pipeline CP readings can be taken in the vicinity of the mat
• Any interaction with the pipeline CP system is eliminated
• The life of the anodes used to protect the mat is significantly increased

Problem:
When pipelines are in a common corridor with energized power lines, electric and magnetic fields can cause unwanted voltage to appear on the pipeline. This induced voltage requires low resistance grounding for mitigation, while cathodic protection demands complete isolation for the pipeline.

Solution:
DEI products provide continuous AC grounding for pipelines with induced voltage, while leaving the cathodic protection voltage unaffected. The device presents low impedance to alternating current and high impedance to direct current, and connects between the pipeline and a grounding system.
 

Mitigation designs for induced AC voltage are best done by specialists trained in the proper analysis techniques. Such analysis involves measurements and electrical modeling, using software developed for this task. While an overview of the issues involved is shown below, complete analysis may involve the use of such specialists.

Small projects can have reasonable estimates applied to determine product ratings and a basic system design. Examine the issues outlined below or call DEI for additional guidance.

To implement an induced AC voltage mitigation system, the following issues
need to be addressed.
1. A suitable low resistance grounding system is needed
2. The Measuring Induced AC Voltage and Current flowing to ground needs to be known
3. Determining AC Fault Current exposure exists and should be estimated
4. Is this site considered a Hazardous Locations Definition?
5. Mounting the DEI device for above-grade or underground connections

See Application Note 6 for a full review of this application, including mitigation considerations.

Problem:
When an insulated joint is used to electrically isolate sections of pipeline, over-voltage protection of the joint insulation may be necessary. The insulation can fail, due to lightning or AC fault current, with potentially disastrous results. Arcing across the joint will cause insulation failure and possible ignition of flammable gases.

Solution:
A protection device connected across the insulated joint will limit the voltage to safe levels, and provide a conduction path around the joint, while maintaining cathodic protection. Products listed for use in hazardous locations will address the over-voltage problem while assuring safe operation.

To implement an insulated joint protection system, the following issues need to be examined to determine product selection and ratings:
1. The maximum DC voltage present across the insulated joint
2. Whether induced AC voltage is present at the site
3. Examine AC fault current exposure
4. Location of the device, and the resulting conductor length
5. Is this site classified as a hazardous location
6. For mounting options, see data on each product page

See Application Note 1 for a full review of this application.