Distributed Vs Centralized UPS System

1. What are the advantages and disadvantages of both design?

2. Is cascading of UPS advisable or applicable?


#1: I believe maintenance cost and manageability is the biggest benefit of centralized UPSes.

One big battery bank is easier to maintain, service, and secure than many smaller units spread out over a wide area.

Ease of scalability may also play a role. Every time you add a camera or switch, a distributed system could prove expensive to grow.

On the flip side, a distributed system may make it easier to manage loads. If one subsystem needs more power, you just locally add bigger/more batteries.

For your #2: Do you mean use both distributed and centralized UPSes at the same time?

Yes. hybrid, since 24/7 surveillance is a requirement.

I think the problem with distributed ups system is that when the ups is not connected to an emergency power line,while on centralized , a short ciircuit on any line will affect the whole system. am i right?

In addition to Brian's excellent points I would add a couple others.

Central UPS Benefits:

  • Initial Purchase Price, dollars per kVA is likely to be lower due to larger cells, as well as shared components like cases, power conditioners, electronics etc.
  • Less Excess Capacity need be purchased. Buying smaller individual units means rounding up to the next highest capacity model on every unit. For instance requiring 600 kVa but having to buy a 800 kVA model.
  • Power can not be dynamically distributed. In a central UPS during an outage, decisions can be made depending on the circumstances and the prognosis for power resumption, to limit power reserves to certain areas over others. All reserves could be directed just to a keeping critical servers running after 10 minutes, say. In a distributed system, it's every UPS for themselves.
  • Single Management Interface
  • More Predictable Uptime, with distributed UPSes determining how long each zone will last can be complicated with various vendors equipment and capacities. For example it may not help if the video wall stays on 30 minutes if the VMS servers only last 20.

Distributed UPS Benefits:

  • No new wiring necessary since units are presumably close to their targets. On the other hand Centralized UPSes still need to deliver the power to where it is consumed. Depending on the topology this can be a large expense in adding dedicated, discrete circuits.
  • Add-Hoc Growth Distributed UPSes can be organically added as a company grows. Centralized UPS requirements need to be carefully forecast at time of first purchase. The penalties for overshooting or underestimating can be large.

By cascading do you mean for redundancy when two similar units are put in series with a 'make then break' bypass switch, i.e, as opposed to a parallel load sharing configuration?

A centralized ups connected to all distributed ups. Is this possible?

It's possible but in my experience, (for data centers at least), it's not the normal way that redundancy is implemented for HA systems. Redundancy is usually achieved by the pairing of two identical units in either a serial cascade or a parallel load sharing scenario.

You could try and cascade several smaller distributed ones into one large one but sizing it properly may be difficult.

Also, it will be extremely hard to estimate your autonomy/endurance as different UPSes engage and disengage from the central UPS. Therefore creating an acceptable SLA may be challenging.

Also, short circuit protection can be implemented by using multiple downstream PDU's.

Can you divulge a little more about the application in terms of load size, load type, topology and emergency power generation?

How many 9's are required for uptime?

Thanks.

five 9's. 20 Distribution Switch (24 port PoE Switch) , 2 Fiber Switch (24 port), 10 PTZ camera, 140 fixed camera, in a 10 storey building

The servers/NVRs and Fiber switches are all together in one room?

How many? Dual corded with dual power supplies?

Dedicated mains circuits to each floor/zone from a central location (server room)?

Diesel generators? 24/7 on-site staff to perform emergency power failover?

Servers /NVRs and Fiber Swicthes are all in the Control Room.

7 NVR/servers

There is a main circuit breaker in the control room for each floor level.

Diesel Generator. There is an on-site staff to perform emergency power fail over.