In regards to the installation of C.P. Sentinel Aqua-Line series rectifier unit(s) and C.P. Sentinel series rectifier unit(s) with potential (reference electrode) control, please note that IRT, as the rectifier manufacturer, shall only be responsible for the proper construction and operation of the rectifier unit(s) in accordance with our rectifier specifications. The methods used during the installation of these rectifiers, including the routing and connection of the external cable connections (Anode, Structure, Reference Electrode & Structure Sense) shall be the responsibility of the Cathodic Protection (CP) engineering and/or service company that has been contracted to complete the CP installation. However, as improper installation and cable routing techniques can adversely affect the operation of these potential (reference electrode) controlled rectifier units, we recommend the installers be familiar with the following guidelines.
- ROUTING OF WIRES:
- Route the Reference Electrode and Structure Sense lead wires in a separate ferrous metallic conduit from the rectifier DC output Anode (+) and Structure (-) cables. The Anode and Structure cables can carry large currents with considerable ripple voltage. If the Reference Electrode and Structure Sense lead wires are run in the same conduit as these cables, they will be closely coupled and may have levels of electro-magnetic voltage induced on them, which in turn will cause erroneous CP system potential voltage readings to be fed to the rectifier controller circuit (and thus, improper operation of the rectifier unit).
- Superior Potential Mode control is achieved by minimizing noise on the lead wires used for the Reference Electrode & Structure Sense connections. It is strongly recommended that lead wire lengths in excess of 25 feet or lead wires in noisy electrical environments be shielded in a separate conduit, and/or consist of shielded, twisted-pair conductors installed using industry standard shielding practices.
- If it is absolutely necessary to route the Reference Electrode & Structure Sense lead wires in the same conduit as either the current carrying Anode or the Structure cable, it is recommended that “both” the Anode “and” the Structure cable be routed in the same conduit. If the potential sensing lead wires are routed with only one of the current carrying cables, significant noise/interference can occur and cause improper operation of the rectifier unit.
- “ON” POTENTIAL CONTROL: “ON” potential control utilizes the voltage measured between the Reference Electrode and the Structure while current is flowing in the CP circuit. “ON” potential control occurs if any of the following parameters in the CP installation are true:
- The automatic controller is configured to sample the Reference Electrode and the Structure continually (jumper JPR361 is installed).
- The rectifier is equipped with an “efficiency filter”, also called a filter choke or an inductor, which stores current energy and allows a continual flow of current in the CP circuit without interruption.
- The rectifier is a three phase unit, where the overlap of the each of the three phases allows for the continual flow of current in the CP circuit without interruption.
- “IR-DROP FREE” (or “INSTANT OFF”) POTENTIAL CONTROL: For IR-Drop Free potential controlled type rectifiers (such as our C.P. Sentinel Aqua-Line series), the rectifier controller removes the IR-drop error from the potential measurement by interrupting the CP current supplied by the rectifier momentarily. This action produces an instantaneous voltage drop, which is considered to be the external IR-drop. The potential voltage from Reference Electrode to Structure is measured immediately after this instantaneous drop, and is considered to be the “IR-Drop Free” potential of the structure. The rectifier controller samples the potential during the portion of the waveform when current is not flowing.
- “IR-DROP FREE” POTENTIAL READINGS: In pipeline type CP applications, if the coating hasn’t deteriorated, it may be hard to obtain a “usable” IR-Drop Free reading because any holidays (defects or damaged areas) in the coating as “seen” by the Reference Electrode may be a considerable distance away. Pipeline installations with FBE coating or other well coated pipelines, could have a voltage drop in excess of 3 volts across the coating in addition to the polarized potential on the steel. In this situation, it is not unusual for the “ON” and “IR-Free” potentials to differ by this amount; depending upon the positioning of the Reference Electrode relative the anodes and the structure (pipeline). Due to this, often in these types of situations, CP engineers revert to constant current control instead.
- POTENTIAL CONTROL MODE LED: The Potential Mode LED on our SentryTM controller will become illuminated only when the structure to reference electrode potential voltage it senses attains the same level as the operator selected Potential “SET” point. Keep in mind, a new, large structure may require considerable time to polarize from the native state. In this case, the rectifier output will ramp up to the current set point (or limit) or the voltage set point (or limit) to try to achieve the potential setting. If none of the Mode LEDs on the controller are illuminated, this means none of the current, voltage or potential set points have been attained. If the rectifier is equipped with range taps (25%, 50%, 75%, & 100%) or manual transformer taps, and is producing some output current and voltage, you may have to increase these tap settings on the transformer to attain the desired operating parameters.
- LOSS-OF-REFERENCE SHUTDOWN: Upon degradation or failure of the Reference Electrode, internal cell resistivity increases, and the “reference” voltage decreases. As the sensed structure to reference electrode potential voltage drops, the proper reaction of a potential controlled rectifier is to increase to full DC output to try to counter the reduced voltage sensed. If this situation continues for a period of time, the coating on a structure can be damaged or fail due to excessive polarization. Therefore, our potential (reference electrode) controlled rectifiers are equipped with a “Loss-of-Reference” shutdown feature. (Refer to the O&M manual for additional information on enabling or disabling this feature). The rectifier “REFERENCE SELECT” switch must be set to sense an active and functional Reference Electrode input, or no output will occur from the unit. A “Loss-of-Reference” shutdown condition will be evident by the digital Potential Meter showing overload (first digit a “-1” followed by remaining digits blank or all digits blinking).