Battery Systems for Mission Critical Infrastructure - Design, Maintenance and Testing (1)

 

Proper design, maintenance, and testing of battery system in mission critical facilities are crucial for business continuity and safety.

In these articles, we are going to

(1) Understand the need for reliable batteries in mission critical facilities;
(2) Explore the most common battery abnormalities that can be spotted through inspection; and
(3) Review simple steps that can be taken to find out battery problems.

When we say the systems are mission critical, it means "Power remains uninterrupted!". But this mission critical label does not apply to every single part of the facility. Some processes are more important to the business than others, and that is where the focus of the design lies. Certainly, designing for a mission critical facility can be challenging. There are many considerations in play. The system has to be very robust with no single point of failure.

Designing electrical systems, maintenance is an important factor, especially in deciding what battery to implement. Maintenance includes but not limits to the cost of replacement of a battery cell. It also involves the accessibility of the battery system, the ease of disassembly and reinstallation, the frequency of service, and the conditions needed in the actual environment (temperature, humidity, etc.).

The goal of maintenance is to prolong the life of batteries and to make sure the batteries perform as designed. Inspection is done to catch any abnormalities that could impact battery performance as well as long-term life expectancy. It is important to place the batteries in an environment that agrees with the manufacturer’s recommendations.


Battery Types


There are several types of batteries used for providing power to electrical systems. The most popular types of batteries being used nowadays are lead-acid and nickel-cadmium (NiCd). NFPA 110: Standard for Emergency and Standby Power Systems defines two types of lead-acid batteries:

Valve-regulated lead-acid (VRLA): A lead-acid battery consisting of sealed cells furnished with a valve that opens to vent the battery whenever the internal pressure of the battery exceeds the ambient pressure by a set amount.

A typical valve-regulated lead-acid (VRLA) battery used in an uninterruptible power supply (UPS) application

Vented (or flooded): A lead-acid battery consisting of cells that have electrodes immersed in liquid electrolyte. Flooded lead-acid batteries may have a provision for the user to add water to the cell and are equipped with a flame-arresting vent, which permits the escape of hydrogen and oxygen gas from the cell in a diffused manner such that a spark, or another ignition source, outside the cell will not ignite the gases inside the cell.

Although NFPA 110-2010 recognizes the usage of NiCd batteries for emergency systems, no definition is provided for such batteries. A definition can be found in IEEE 1106-2015: Recommended Practice for Installation, Maintenance, Testing, and Replacement of Vented Nickel-Cadmium Batteries for Stationary Applications (https://standards.ieee.org/findstds/standard/1106-2015.html).


Battery Uses


Mission critical facilities are not only the buildings that are critical to human life, such as hospitals, but also are facilities for business continuity, like data center. Many methods are employed to mitigate the risk of power outages. But, almost always, the risk mitigation relies upon batteries. Uses include:

Uninterruptible Power Supply (UPS) Systems: Batteries are used to back up power where UPSs are involved. While the power is processed and converted through the UPS to the load, the batteries are kept charged to provide the much-needed power to the critical system when normal power is out. Even though standby generators are most likely used as backup power, the batteries provide the critical power needed until the generators are able to receive load.

Standby Generators: Batteries are used to provide the initial crank to the generators as well as power the generator controls.

Controls: Batteries also are used to back up controls, especially when medium-voltage distribution is found throughout the facility. Nowadays, the operation of critical systems is more reliant on controls to avoid nuisance tripping and to enable fast-acting protection.

Emergency Systems: Batteries are widely used to back up life safety systems, such as exit lights. Exit lights normally are backed up by a 90-minute battery to allow people to recognize the way out of the building in case of a life-endangering situation. All of the above-mentioned uses (UPS, generators, and controls) could be part of an emergency system as well.



Next Article:
Battery Systems for Mission Critical Infrastructure - Design, Maintenance and Testing (2)



About us

SMA connects IT, Facilities and Design. For the other design considerations, please visit 

(1) Site Selection,
(2) Space Planning,
(3) Cooling,
(4) Redundancy,
(5) Fire Suppression,
(6) Meet Me Rooms,
(7) UPS Selection,
(8) Raised Floor,
(9) Code & Standards,
(10) Transformers and Harmonic Distortion,
(11) Multi-mode UPS Systems,
(12) Electrical Rooms,
(13) Generator Systems,
(14) Generator Fuel Systems, 
(15) Battery Systems, etc.

All topics focus on key components and provide technical advice and recommendations for designing a data center and critical facilities.

Strategic Media Asia (SMA) is one of the approved CPD course providers of the Chartered Institution of Building Services Engineers (CIBSE) UK. The team exists to provide an interactive environment and opportunities for members of ICT industry and facilities' engineers to exchange professional views and experience.

Critical Facilities & Data Center Design Consideration: Generator Systems Design (1)

Let's recap the basic concept of mission-critical facilities:-

(1) Uptime Four-Tier Levels
(2) Critical Supply Diagrams and Configurations

The terms “N, N+1 and 2N”, typically refer to the number of power supply and cooling components that comprise the entire data center infrastructure systems. An “N” system is not redundant at all. N+1 and 2N, represent increasing levels of component redundancies and power paths, roughly mapping to the Tiers 2-4.

A paralleled generator system uses two or multiple generators to form a large-capacity generator system. Paralleling multiple generators is achieved by synchronizing the output of the generators and connecting them to a paralleling switchgear (PSG) common bus. Synchronizing the output of the generators requires all of the paralleled generators to have the same voltage, frequency, and phase rotation.

With closed transition back to the utility, PSG will parallel the generators and synchronize the generator output with the utility source for a short duration before transitioning back to utility power. When connecting the generators in parallel or synchronizing with the utility, the following criteria must be met:

• Matched / proper frequency
• Matched / correct phase rotation
• Phase voltages in phase and within specified voltage range

Typical parameters that determine synchronization include a voltage difference of less than 5%, a frequency difference of less than 0.2 Hz, and a maximum phase angle of 5 electrical degrees between the sources.

Closed transition is used when it is desirable to transfer loads with zero interruption of power when conditions permit. It is used when the generator system transfers back to the utility and when load testing the generators with building loads. Closed transition can be either a soft load transfer or a make-before-break transfer. The PSG soft-load transfer synchronizes and operates the generators in parallel with the utility and transfers loads in increments between the two sources, thereby minimizing voltage or frequency transients on the generator plant and utility distribution system.

The typical soft-load-transfer overlap time is around 2 seconds. The make-before-break transfer will parallel the generators and perform a transfer of load from the generator to the utility. This can be the transfer of one large block load or the transfer of multiple block loads having time delays between the block loads. Time-delay transfer can either be programmed through the PSG or the downstream automatic transfer switches (ATS). Typical ATS make-before-break transition overlap time is usually less than 100 milliseconds.


To simplify the design of a paralleled generator system, identical generators should be used with the same manufacturer, ratings, type, output rating and alternator pitch.

If paralleling of dissimilar generators is required because of existing onsite conditions, the design of a paralleled generator system becomes much more complex. Each generator configuration must be evaluated and dissimilar components, such as speed control, voltage regulation, and alternator, must be retrofitted to match.

"Pitch" is the term used to define the mechanical design characteristics of the alternator. Paralleling a generator of 2/3-pitch alternator design with a generator of 5/6-pitch alternator design will result in circulating neutral currents. The circulating current will be disruptive to protective device operation and may damage alternators.


Configurations


The electrical loads must be classified into emergency loads, required standby loads, and/or optional standby loads that classified loads are separated, and the generator sets are sized so one generator can serve the emergency and required loads purpose.(see the following Figures)

One generator supplies emergency power to emergency loads, required standby loads and optional standby loads.

Multiple generators in parallel supply power to emergency loads,  required standby loads and optional standby loads.

Kindly note paralleled generator systems that rely on a single master control for signals to start and close to a paralleled bus actually replace one failure point with two, as the master control and the communication link between the master control and the generator systems each represent Single Points of Failure. A well-engineered paralleling system will have dual hot-backup control systems, redundant communication pathways, redundant best battery select dc power supplies, multiple breakers, multiple power pathways, and a well-documented procedure for system recovery whenever a component fails.

Benefits of Parallel Generator Systems


Paralleling multiple sources provides increased reliability, flexibility in load management, and maintenance capabilities with little to no disruption. Multiple generators paralleled to a common bus can better serve emergency and business critical loads, particularly for system response time and dynamic load response once in operation. However, more complex, parallel generator standby systems have significant advantages with respect to reliability and redundancy. These advantages include redundancy, efficiency and ease of maintenance and serviceability.

Redundancy: 

The redundancy inherent in the parallel operation of multiple generators provides greater reliability than a single generator unit for critical loads. If an N+1 configuration is adopted, one generator can be offline for maintenance while serving the required loads. Furthermore, providing a running spare, an N+1 generator configuration will increase the reliability of the generator system from 98% to 99.96% reliability.

Efficiency: 

Variations in power demand can cause a single larger generator to run at loads of less than 30% of capacity. The optimum operational point is between 75% and 80% of its rated value. The paralleling control system can be equipped with a generator load control that can add and remove generators in response to the actual load/demand of the system. If the load changes and demand reach 90% of running capacity, for example, an additional generator can be started, synchronized, and paralleled to the bus with no time delay.

Maintenance and Serviceability:

Maintenance can be performed without interrupting the availability of the generator system because one generator can be removed from the system to undergo scheduled or unplanned maintenance while the other generators are available to supply the loads.



Go to the next articles:
Generator Systems Design (2) - Generator Ratings
Generator Systems Design (3) - Generator Sizing


About us

Strategic Media Asia (SMA) is one of the approved CPD course providers of the Chartered Institution of Building Services Engineers (CIBSE) UK. The team exists to provide an interactive environment and opportunities for members of ICT industry and facilities' engineers to exchange professional views and experience.

SMA connects IT, Facilities and Design. For the other design considerations, please visit 

(1) Site Selection,
(2) Space Planning,
(3) Cooling,
(4) Redundancy,
(5) Fire Suppression,
(6) Meet Me Rooms,
(7) UPS Selection,
(8) Raised Floor,
(9) Code & Standards,
(10) Transformers and Harmonic Distortion,
(11) Multi-mode UPS Systems,

(12) Electrical Rooms,

(13) Generator Systems, etc.

All topics focus on key components and provide technical advice and recommendations for designing a data center and critical facilities.

Diesel Fuel: How Critical for your Standby Power?

Data center downtime is a familiar topic in the industry; however avoiding down time through proactive fuel management is not common knowledge in the field despite an emerging relevance. A vast majority of data centers use diesel to supply their backup power systems.

Historically diesel could be stored for extended periods at a time and function smoothly when needed. Unfortunately, this is no longer the case. The environmental burden of diesel has been reduced by government mandates reducing the sulphur content of diesel and introducing bio-diesel blends. However, in doing so, the need to manage stored diesel has surfaced.


Changes in Diesel

The process to remove sulphur in diesel can affect the functionality of the fuel, to compensate, refiners include additives. Some of these additives, such as certain forms of lubricants, de-icers and bio-diesel itself increase the ability of the fuel to absorb water.


Effects on Your Generator

Water in diesel causes problems and subsequently leads to diesel generators either not kicking in, or failing mid-operation, when standby power is needed in emergency backup situations. It will be a disaster situation when data centers and other critical facilities, such as hospitals, faced severe down time as a result of backup generators not functioning as expected.


Fuel Management: Fuel Testing

A comprehensive fuel management strategy begins with knowing what type of fuel you have, and the state it is being stored in. Research into bio-diesel mandates in your area and perform regular onsite and offsite testing to see the bio-diesel, water and microbial contamination of your fuel (microbial growth is a sign that troubles lie ahead).


Fuel Management: Fuel Polishing

According to Polaris Laboratories, “in systems prone to water contamination,” (such as fuel storage tanks) “it is imperative that the contaminated oil be able to shed water, or demulsify in order to maintain lubricity, viscosity and prevent the formation of acids.”


To begin creating a fuel management protocol, evaluate the tank, piping and generator set up to highlight areas of weakness; consider the impact of likely site temperature and humidity ranges.


The Uptime Institute’s technical paper, titled Biodiesel, suggests finding a fuel polishing system utilizing coalescing filters which have been proven to remove water suspended within the fuel (emulsified water). An automated fuel polishing system is recommended; continuously remove water and particulates, ensuring emergency ready fuel all the time.




About The Blogger


Strategic Media Asia (SMA, www.stmedia-asia.com) is a leading technical training and event organizer for corporations specialized in data center design & build, E&M facilities, telecom, ICT, finance and colocation. Currently, SMA delivers a series of data center trainings and qualification programs in Hong Kong, Taiwan and Macau.

All these events / training seminars are designed to support the leadership needs of senior executives (Chief Information Officers, IT Directors / Managers, Facilities Managers, company decision makers, etc.) and to provide useful and applicable knowledge.

For detail, please visit our data center courses & training seminars at http://www.stmedia-asia.com/trainings.html.