Power Monitoring System GPS Clock 4

[Bilegan]

What is the purpose of a PMS GPS clock? If it is required, what are the parameters to be considered?

We will design the electrical system of an additional complex in an existing facility. The PMS will supervise, control and monitor the operation of HV/LV X'formers, switchgears, MCC's, and UPS in the new S/S and PIB's. The additional complex will require 2 new S/S, and they are 500 meters apart. One of the new S/S will derived its source from an existing S/S, 1.5kM, via underground cables, the existing S/S is equipped with PDMS.

Bilegan

 

[dpc]

The main reason is to have a precision time source that is used to synchronize the internal clocks in the digital relays and other devices. This is done via an IRIG input into the relay from the clock.

Like your computer's internal clock, the relay clocks will drift over time. When reviewing fault data, it is extremely helpful to have all of the relay event reports synchronized to the same time. For this purpose, the GPS clock is highly desirable, but not mandatory.

If you are planning to do anything with synchrophasors, the GPS clocks and IRIG interface wiring are mandatory.

 

[Bilegan]

Thank you DPC, your input is valuable, it will be a very good start for me to understand gradually the importance of GPS clock in the expansion project of our existing facility.

To all other valuable contributors of this forum, please share your technical experience about GPS clock.

Thank you in advance
Bilegan

 

[bacon4life]

In addition to timestamping relay event reports for protectioni engineers, using GPS time stamps for all SCADA data allows dispatchers to see the correct sequence of events system wide, even though we have vastly different polling rates across the system.

 

[slavag]

Small additionals.
1. For TOU of metering for example ( time of use).
2. For fault recorders/transient recorders
3. For part of 87L ( line differntial protection).
Regards.
Slava

 

[Bilegan]

To bacon4life, thank you for the additonal info, it helps.

To Slavag, i want more technical elaboration from you. I read your technical responses to the many discussions posted here and they are very impressive to the point that they are quite acceptable.

 

[slavag]

Hi Bilegan.
Thanks a lot for your words .

If you need more info from me, firstly, I need more info from you. What is a type of eq. you will use, what are protocols, what type of GPS, etc..?

Best Regards.
Slava

 

[Bilegan]

The intention of PMS requirement is to dedicate a stand alone system for monitoring and data collection. It is allowed, and sometimes required, to interface the PMS with other systems such as Distributed Control System (DCS), protective relaying, Supervisory Control and Data Acquisition (SCADA) system, etc. PMS is considered a stand alone system even though it is allowed to be interfaced with other systems.

The time synchronization mechanism of the PMS shall be automatically activated every hour to synchronize system components (server, database, and field monitors). Tolerance in time differences between system clocks shall not exceed 1 millisecond. A Global Positioning System (GPS) clock is used to broadcast system time to the PMS components.

The PMS shall have a dedicated (private) Ethernet network that serves as communication link between the monitors and system server(s). The PMS server can be connected to proponent's LAN/WAN to provide access for PMS clients using proponent's network. PMS is considered a stand-alone system even though it is allowed to be accessed by clients using the public network.

The Database management system shall be configured to perform the following tasks:
1 Automatic data backup.
2 Archive the data; data older than one year shall be automatically archived in a permanent storage media.
3 Maintain a minimum capacity of one (1) year worth of data to be always available in the online database (hard disk).

Returning back to my original question, the existing S/S which will served as a tie-in point for the power supply of the new complex has no PDMS or PMS or clock.

Do we really still need to install a GPS clock for the new PMS of the new complex?

 

[dpc]

If you want time accuracy of one millisecond between device clocks, you need a GPS clock and IRIG-b.

But if you don't want one, I don't think anyone here is going to force you to get one.

 

[slavag]

Hi.
If you want time accuracy, yes, you need GPS, if no, you have option synchronization by Ethernet, by own protocols of power meters. Isn't 1ms, but more than enough. Next point, if it's only power metering data, not billing and not power qulity , you don't need any synchronization, your server polling all data and put it to database with timestamp of server.
Best Regards.
Slava

 

[Bilegan]

A very nice one from you again dpc.

My understanding is depend now from the proponent of the new complex if they push us to provide the GPS clock.

I will wait for the information of other technical guys in this forum to share their experience and expertise.

Regards,
Bilegan

 

[Bilegan]

I am weighing your above explanations, it seems GPS clock is required.

dpc and slavag are the same opinion in time accuracy requirement.

Three (3) pointer of slavag; power metering and power quality are manadatory (2), power billing (1) is not required.

Regards,
Bilegan

 

[Jebb]

If you are looking for a 1 ms accuracy you probably need to broadcast the time from the GPS clocks to the PMS devices more than every hour. In the system we use for time synchronization we've determined that a time broadcast every minute works very good to keep all the "clocks" in sync. Depending on the method the individual equipment uses to keep the "clock" going we've discovered that diffrent equipment can drift as much as 2-5 ms over a 1 hour period. We use a GPS clock connected to a host machine using the timeserv application to broadcast it to all the other local equipment. GPS clocks are relatively cheap so we've deployed them at each of our stations over our network (10's of km). This has saved us may of time when when we're trying to fault trace an event...

 

[slavag]

Jebb is correct.
For this used term PPM pulse per minute.
But still Im very scepty for the 1ms accuracy, I would prefferd used 1ms resolution.
Best Regards.
Slava

 

[Bilegan]

Jebb, in our case, 3 Substations are involved in the project, 2 are new S/S to be constructed and the other is existing S/S. For time being, we will assign tag for the S/S's.

Let us say;
S/S-A; Existing (Tie-in of S/S-B)
S/S-B; New (S/S-B, Feeds S/S-C)
S/S-C; New

Note, each of S/S has 2 new PMS to be installed.

How many GPS clock each of S/S required to be installed, if every S/S (existing & new) has 2 PMS, Do I need to install GPS clock in each PMS?

Slavag, can you please explain further your opinion in your last post. Is there any impact to my question about "When is a GPS clock requires in the PMS".

Regards,
Bilegan

 

[davidbeach]

One clock can feed IRIG-B signals to all equipment. I'm aware of a clock available for as little as $550 US. Why not install a clock instead of fighting it?

 

[slavag]

Hi Bilegan.
As far, as I understood from your previuos posts:
You have 3 SS, PMS in each one is stand alone system with dedicated computer and with some interface to ohter SCADA or DPMS or DCS system.
If you need time synchronisation, prefered dedicated GPS to each computer.
PPM will provided by two ways or by some digital signal or by soft. This point you have check with PMS supplier.
Usually, in new system, is build-in broadcast command via communication lines, as Jebb wrote. PMS system usually have few options for the time synchronisation or IRIG-B or SNTP
(LAN-time). Possible installed some GPS card (PCI card into computer), BTW cost of antenna, cable and card not so expensive. Maybe PMS supplier have a own solution.
Again, for the only trends of analog values and TOU you don't need 1ms accuracy, you can sinchroniesad system by Ethernet, accuracy will be +/- 20-30ms.
What I meant: accuracy and resolution. It's hard explain for me. Simple for 1ms accuracy, you need dedicated sinchronisation bus (IRIG-B for example) with input to every
meter or minimum to master switch. 1ms resolution is only timestamp with xx.xx.xx.xxx ( hours, minutes, seconds, miliseconds)
Best Regards.
Slava

 

[Bilegan]

Thank you dpc for your prompt reply. with your initial info. it helps me to dig deeper how a GPS clock works.

Thank you too Slavag, your elaborations, options and solutions are valuable.

To Jebb, he gave me a picture that GPS clock can be installed on every ststions. It helps.

Davidbeach is correct when he point out that one GPS clock for the whole system is enough.

It was decided in our project to utilize the existing GPS clock, and modify the hardware and software of the existing PMS system to suit our new requirement.

Regards,
Bilegan

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