PRP and HSR

The question was asked "What is the basic difference between PRP (Parallel Redundancy Protocol) and HSR (High availability Seamless Redundancy)". My response was:

Very simply PRP is a duplicate network of whatever design you have (could be rings, mesh or star), while HSR is a ring network. I've seen PRP used in a star configuration, and I think that is its real strength as it is simple.

HSR is the 'zero delay' alternative to RSTP for rings, but does require the use of Redboxes or devices with native support. Quite a few switch manufacturers have embedded modules that provide HSR or PRP functions, or you can purchase code for FPGAs from a number of vendors and use it directly in your device.

@Rod, perhaps in the utility world duplicate protection is the norm, but this is not the case for distribution and industrial applications.

HSR and PRP have application where network based signalling is used and there is a need to maintain the Ethernet switches. With copper signalling each connection is independent, but with Ethernet a switch will affect multiple connections.

RSTP is ambiguous enough with each vendor having differing parameters and their own tweaks for speed. HSR gives more deterministic performance, and PRP avoids slow recovery times with multiple meshes. A second switch is cheaper than duplicating all the protection, and many vendors are supporting HSR/PRP even in their 'low end' devices.

@Rod, I agree that an engineering design (requirements spec, cost/benefit, failure mode study) should be undertaken for any substation LAN design. Unfortunately this doesn't happen.

For small rings RSTP can work fine, and quite a few vendors have dual port IEDs so switches are not required. The hardware cost to go to HSR is minimal (some FPGA code) since there are already two ports on the device. The 'integrated' switch for ring applications has been around for some time (HiPER Ring, MRP, RSTP) — I don't think HSR/PRP has been driving it. For large rings MRP and HSR have definite speed advantages by knowing the topology is a ring. RSTP is more flexible, but that flexibility slows things down.

BTW, as far as integrating protection into a MU — great idea, shame that one of the large European manufacturers is trying to patent this as their own clever idea.

@Juan, differential protection can work through the exchange of phasors too. 64kb/s channels (C37.94 or G.703) are not really enough for raw values, so IEDs process the samples to get the data rate down to a level that can be transmitted.

I think that “Protection Computers” will ultimately do what you propose. ABB already do this with protection of their SVCs, and a Dutch company has a range of products for distribution based on distributed sampling and central protection (but not using 61850). I forget the name at the moment. The substation of the future will have merging units in the field, a few Ethernet switches and two protection computers to do the thinking. The control room can be replaced with a telephone box sized panel!