Battery Monitoring for NERC Compliance

The VIGILANT® system includes the following main 4-5 components:

• VIGILANT® Monitor – Stores data, runs web-server, handles communications. (1) monitor per battery system.
• VIGILANT® Sensors – Measures cell/unit parameters. (1) per cell/unit, plus (1) per string.
• Connection Hardware – Physical connection to battery post. (2) clamps or (3) tab washers per cell/unit.
• Wiring Harnesses – Connects VIGILANT® sensor to battery connection hardware. (2) harnesses per cell/unit.
• Electrolyte Level Sensors (optional) – Measures electrolyte level, (1) per cell.

This depends on the model of the VIGILANT® or the chosen method to power the monitor. The system can be powered off the battery or from an external power source. Below are the options to power the system:

From the battery:

• Low voltage: 36 – 72 VDC
• Medium voltage: 95 – 300 VDC
• High voltage: 280 – 580 VDC

External:

• 24 VDC (often used for AC power with a converter)

No, all VIGILANT® components are powered from the monitor, which receives power from the battery charger or an external power source.

The VIGILANT® monitors the following parameters at the specified interval:

• Battery float voltage (15 min.)
• Charger float voltage (15 min.)
• Float current (15 min.)
• Charge & discharge current (1 sec. during discharge)
• Ambient temperature (15 min.)
• Cell/unit voltage (15 min.)
• Cell/unit resistance (Once daily)
• Interconnection resistance (Once daily)
• Terminal resistance (Once daily)
• Negative post temperature (per every cell/unit) (15 min.)
• Electrolyte level (15 min.)
• Ground fault (15 min.)

Yes, the VIGILANT® monitors the float current in the battery by accurately measuring the potential difference across the cell interconnections; this enables reliable detection if the battery has a continuity fault. In addition, we rely on the ohmic readings from each interconnection.

The ohmic value of a cell or unit reading can be reported as Resistance, Impedance or Conductance and which value reported is dependent on the perturbation method used. If a DC source is used, the value reported will be a Resistance. If an AC source is used, the value will be reported as Impedance. Both these methods are reporting the change in ohmic value as an increase in the opposition to current flow, whereas Conductance, which is the reciprocal of Resistance, will report the value in siemens or mhos and the value will drop as the battery ages.

In the thirty plus years that ohmic values have been part of a battery maintenance program, while the individual test equipment manufacturers have promoted the value of their specific method and while the values reported will be different, their ability to identify the level of change is virtually the same.

The VIGILANT® uses a DC perturbation pulse, so it reports the value as a resistance.

The VIGILANT® was designed to incorporate the ELM-Series electrolyte level sensors. Each ELM sensor plugs directly into the Vigilant sensor for that cell. This allows the software to display which cells specifically have low electrolyte level alarm. These alarms can be cleared from the software or in the field after a cell is refilled.

Typically, battery ground voltage (without fault) should sit midway between battery positive and negative. The VIGILANT® checks the ground potential relative to the battery mid-point and will detect an imbalance if the ground potential is not mid-battery voltage. The closer the ground fault to battery positive (or negative) the signal will have a higher ground leakage current. When measuring for a ground fault the VIGILANT® is looking for a nominal difference of 9% (not adjustable on present system). This to say, on a 120V system with the battery mid-point at 60V, if the ground voltage is below 54.6V or above 65.4V then a ground fault warning will be raised.

Be aware that some systems have one battery terminal intentionally grounded (usually positive on telecommunication systems). If this is the case then the small green wire loop in the monitor should be removed, or, do not ground the monitor chassis. This will prevent the monitor recording a ground fault.

No, this has been tested with most battery chargers on the market and there has been no conflict.

Each sensor draws a robust test current for a very short time from each cell, this results in a small momentary change in the terminal voltage. The waveshape and parameters of the change in the terminal voltage are analyzed, and from this the VIGILANT® can determine the cell and strap resistance.

The sensors analyze the cell energy and automatically optimize the test current to maintain a safe level of test. The actual energy drawn from the cell during the test is insignificant to the battery and is not detrimental to the cell in any way.

Standby batteries are subject to a float current all their service, lives in order to maintain them for instant use. The resulting float voltage is actually an overvoltage of approximately 150 millivolts per cell on top of the cell’s fully-charged natural open-circuit voltage.

Cell internal resistance/impedance is calculated by drawing a current from the cell in a pulse pattern and measuring the change in the terminal voltage. If too low a test current is used, several factors which can adversely affect the measurement come into play

• The change in terminal voltage will be too small to come from the cell itself, but will come from the overvoltage, mainly influenced by the charger. If the float current changes the measurement will be different.
• Battery system noise and ripple can obscure a small test current and lead to adulterated readings
• A low test current means a small response signal; the smaller the signal the less accurate the measurement can be.

Yes, a temperature sensor is built into every negative post connection from the VIGILANT®. It is recognized in the battery industry that the negative post of the cell is the most sensitive to internal temperature variation, and if ‘acid creep’ is experienced it is inevitably at the negative terminal post first. The negative post is often at a slightly higher temperature than the positive post and in any case terminal posts are a much better indicator of internal temperature than the plastic cell casing, which is a thermal insulator and influenced by the ambient temperature. The VIGILANT® sensor is designed to have an excellent thermal connection to the negative post and is also insulated against the effects of changes in the ambient.

No, the VIGILANT® does not influence or have any effect on the cell/unit voltage. The system is designed strictly for data acquisition and is not intended to change the battery in any way.

While not directly measuring sulphation inside the cell, the VIGILANT® measures parameters which can indicate sulphation is present.

In a lead acid battery, when it is discharged, both the positive and negative plates will be converted to Lead Sulphate and return to Lead Dioxide and Sponge Lead when they are recharged. It is important that the battery is recharged as soon as possible, as the lead sulphate will crystallize over time, at which point no amount of recharging will change it back to its original fully charged state.

If the battery is not being charged at a high enough voltage to overcome self-discharge, lead sulfate will form on the plates, initially on the edges but eventually on the surface of the plates, and when it crystalizes, it will block the underlying active material and reduce capacity. Although in the initial stages it will not change the Ohmic measurement, once it affects the surface of the plates it will. Monitoring the individual cell/unit voltages to ensure that they are within the manufacturer’s limits should reduce the potential for Sulphation to occur. A rise in Ohmic value can be indicative of sulphation and prompt inspection of the cell/unit.