QNX operating system

I worked in the QNX platform when I am dealing with IED simulators. So I thought to write some information about QNX operating system and state resourceful links.

In IED environment priority scheduling is really critical. Breaker tripping and relevant communication should gain highest priority when fault is detected by relay hardware. to fulfill this fast operation IED uses RTOS (real time operating system).Its ultra-reliable nature means QNX software is the preferred choice for life-critical systems such as Power grid,air traffic control systems, surgical equipment, and nuclear power plants. The QNX Neutrino RTOS is the latest incarnation of the QNX real time operating system, which has been powering mission-critical application. The QNX® Momentics® Tool Suite is a comprehensive, Eclipse-based integrated development environmen. Companoes rely on  QNX® Neutrino® RTOS and the QNX® Momentics® development suite to build products that enhance their brand characteristics – innovative, high-quality, dependable.

Socket programming in QNX

When I wanted to compile NetPIPE latency measuring tool on QNX platform. It gave me warnings saying listen(), bind() methods are undefined. I figured out that socket libraries are not linked in NetPIPE make file.
The QNX TCP/IP socket interface is a set of library functions and header files. All memory models of the socket interface library are provided. They're called socketx.lib, where x denotes the memory model. For a description of memory models, see the documentation for the cc utility.
These libraries are installed in the /usr/lib directory.The header files are installed under the /usr/include directory.

Then I added below line to NetPIPE make file to link socket libraries and it compiled perfectly:

cc -l socket

Using IPERF

Iperf is a tool to measure the TCP bandwidth and the quality of a network link.

The quality of a link can be tested as follows:
- Latency (response time or RTT): can be measured with the Ping command.One way Latency can be measured by NetPIPE
- Jitter (latency variation): can be measured with an Iperf UDP test.
- Datagram loss: can be measured with an Iperf UDP test.

Iperf can be installed  on any UNIX/Linux or Microsoft Windows system. One host must be set as client, the other one as server. Clent send predefined size of packets from client to server. Sever receive packets sent by client and measure time taken to collect packets. By dividing total packet received over time taken, iperf decide throughput measurement.  

By default, the Iperf client connects to the Iperf server on the TCP port 5001 and the bandwidth displayed by Iperf is the bandwidth from the client to the server.
If you want to use UDP tests, use the -u argument.
The -d and -r Iperf client arguments measure the bi-directional bandwidths.

For TCP measurement I used,

Server side:
iperf -s

Client side:
iperf -c -F -m -M

Job serach for Smart grid engineer

Alberta :
subnet

Ontario:
Hydroone

Instrument transformers CT and VT

CT types : Bushing type, Bar type, window

VT Types: Electromagnetic VT, Capacitive VT

Directional relays

Types of directional relays:

• Directional over current
• Directional ground
• Directional comparison

MTA - Maximum Torque angle

Over current protection

We need relay coordination to minimize the disruption due to fault and operate the nearest relay first. We can not coordinate fuses because the melting time is fixed.

For Fuse:
total clearance time = pre arching time + arching time
The time current characteristic of a fuse has two curves - minimum melt curve and total clearing time

Sectionalizers  can not interrupt a fault. It counts the number of time it seen the fault and operate after preset number. Reclosers have limited fault interrupting capability.


Types of over current protection:

1.  Instantaneous relays - current only ( can not discriminate the fault currents If1 = If2)
2.  Definite time relays - time only ( Faults near to the source has higher currents and it also show higher time)
3. IDMT inverse definite minimum current relays - both current and time

Consideration of  coordination:

• Maximum and Minimum momentarily Short circuit current
• Maximum and minimum ground fault current
• Total time interval

Coordination parameters

• TAP value (pick up current in secondary CT) - Pick up current
• Time Dial (TD) - Time multiplier setting (MTS) or time dial setting (TDS)
• Instantaneous TAP (IT)
• Extremely inverse characteristic

We use extremely inverse relay characteristic in the industry. There should not be any crossing between fuse characteristics and relay characteristics ( we can adjust this using the correct TDS in the relay.when TD is increased it will become more inverse ). It means fuse characteristic always has to be lower than relay (0.20 s gap). If we coordinate two over current relays their characteristic should have 0.4 s gap.

With CT ratio 500:5  and TAP value 5 means.
Pick up current in CT secondary = 5A
Pick up current in CT primary = 500 A

Fault Calculation

To obtain more accurate results calculation has to be carried out in different time ranges

• Sub Transient- large current 50 ms
• Transient - after 0.5 s
• Steady state- after 1 s

When we analyze large systems with different voltage levels we use base quantities and per unit values .Decaying DC component is considered using the asymmetric factor. Understanding the positive, negative and zero sequence components are required in unbalanced faults.

• For transmission lines positive and negative impedance are same and equal to the per unit impedance of the line. Zero impedance depends on the grounding configuration. Therefor obtain it from manufacture data sheet. 
• Balanced generator only generate positive sequence voltage.
• For motors has same positive and negative impedance. Since most of the motors are ungrounded it doesn't has a zero impedance.

L-L-L or L-L-L-G  => positive sequence
L-G => positive, negative, zero in series
L-L => positive, negative in parallel
L-L-G => positive, negative, zero in parallel

Line to ground voltage = line to line voltage / root(3)

Aspects of Protection system

Reliability

• Dependability - protection should operate when it should operate
• Security - protection should not operate when it should not operate

Speed
We need fast protection to minimize the damage

Selectivity/Discrimination
Zones of protections are determined by the CTs
Understand the type of the fault and fault location

Cost
Cost/beneficial analysis
fast operation and duplication require additional cost
Back up protection

ANSI reference numbers
21 - Distance relay
50 - Instantaneous over current
51 - time delayed over current
52 - circuit breaker
67 - Directional over current
87 - Differential

Faults in power systems

There are two categories of faults:

• Active Faults : Current flow from one phase to another or phase to ground. Two sub categories solid faults(complete breakdown of insulation) and incipient faults(faults start from very small beginning).
• Passive Faults : These are not real faults, but stressing the system to its maximum capacity, and ultimately active fault occurs. (Overloading, over voltage, under frequency and power swings)

Transient Faults : do not damage the insulation permanently and allow the system to re energized after a short time period (lightning strike, momentary tree contact)
Permanent faults : does not disappear when the power is disconnected. equipment has to be repaired.

Symmetrical faults are balanced faults. Sinusoidal are equal about their axis. represent steady state operation.
Asymmetrical faults displays a dc offset and become a symmetrical fault after some time

Availability of hardware in substations

The software and hardware in the substation are designed in a way that they meet high availability requirements. The means high reliability ( Long mean-time-to fail MTTF) and short down time ( Short mean-time-to recover MTTR). MTTF means statistical time until component need a repair.Short down times can be achieved by extensive diagnostic functions, modular hardware designs, fast reconfiguration and automatic restart after a power supply failure.

The redundancy recomended:

• Repair faulty parts in process and bay level in less than two hours and less than 4 h for station level.
• Standby hardware exist physically connected and per-configured.
• Warm standby - standby HW constantly supervise active HW, automatically takes over in a failure. Time stamped events may be lost. commands are reusable after 10-30 sec
• Host standby -  standby HW constantly supervise active HW, it takes over in a failure. No Time stamped events  lost. commands are reusable after 1-5 sec. at bay level switch over time is less than 100ms.

Self supervision of IEDs

• Insensitive against EMI
• A/D conversion may subjected to aging should be supervised by a reference signal
• Watchdog should supervise the response time from processing algorithms
• Checksums are used detect failure in mamory
• Loss of power should be checked

Supervision of communication:

• All communication devices ( Star couplers, routers, switches) are subjected to self supervision
• Detection of errors, check the response time and counting lost messages

Communication requirements of Substation Automation architecture

Introduction of microprocessors in to substation allows process data in digital form. to convert analog data in to digital ADCs are used. These digital data is not distorted due to aging of the hardware and can easily exchanged  by serial communication. But these serial communication introduces additional delays.Also information processing hardware must withstand harsh environment in the substation, specially EMI.
The data is acquired at the process level by means of remote i/o units (RIO) and intelligent sensors (PISA = process interface for sensors and actuators). The process bus connects them to the bay level equipments.

Communication requirements:
Maximum allowed age - worse case response time can be tolerated. This means, that this time must be guaranteed in normal operation.
Data integrity - degree of communication safety in the case of disturbances. If data is directly influence the process those data has higher integrity.
Exchange method - Spontaneous mean communicated as soon as it happens. Request means communicated on request by some function or human.

Alarm - 1s - Medium - Spontaneous
Commands - 1s - High - Spontaneous
Process sate data -2s (binary) 5-10s (measured) - Medium - Spontaneous (gives overview of the process state)
Time stamped events - 10s - low - On request (used for later analysis)
Interlocking data - 5ms - high - Spontaneous (used to prevent dangerous commands)
Interlocking data (state info) - 100ms - high - On request
Trip from protection - 3ms - high - Spontaneous (used to clear faults)

The actual communication throughput capacity must be higher than needed for normal operation( at least 10% higher). When we design the communication system we should avoid the single point of failure.
No communication message failure shall lead to a unsafe action. This can be tackled using communication error detection mechanisms and making transmission media immune to disturbances( reduce number of bit errors). Today all process buses are typically a Hamming distance of at least 4 - 6, to detect transmission errors. This is sufficient for medium integrity. In substation error rate is higher than the telecommunication environment. There for we use glass fiber in the process bus and special communication procedures like "select before use" is introduced.
No lost or late message is allowed to lead to unsafe action.Messages could be lost due to buffer overflows or overloaded routers and switches. There for lost messages and loss of message source should be detected. In IEC 61850 topical flag is used to indicate data is up to date.Glass fiber can cover a distance up to 2000m with out loosing transmission speed. while plastic fiber is used for shorter length( tenth of meters). Also plastic fiber is aging sooner than glass.

Today we can place the microprocessor based relays close to the process. In new architecture physical signal marshaling is replaced by logical signal marshaling, which means complexity is the same. Electrical CAD systems are replaced by signal engineering tools.

For redundancy we duplicate the protection devices at least in HV substations.
To provide passive safety in logical nodes it sends at least two telegrams before a command is executed. This two step approach is called select before approach (SBO). HMI send the select command to CBC node. Then CBC sends selected command back to HMI. Then only HMI sends the operate command to the exact switch.

Substation Automation Structure

Business benifits of substation automation are :

• Better information, Higher productivity
• Intelligent automation, Higher productivity and higher availability

Substation automation structure include Station level, Bay level and process level.

Station Level provides Remote communication to Network control center (NCC) ,HMI, Station level automation, data evaluation and archiving, condition monitoring, events and alarms, station level protection and  Data exchange. Station level equipments are always separated in to two rooms - operation room and the communication equipment room.
Bay Level provides bay level automation, time synchronization, condition monitoring, bay level protection, bay level control, object protection and data acquisition.

Process Level includes GIS or AIS switchgear, instrument transformers, power transformers and surge arresters.Output of VT (100v or 200v) and CTs (1 or 5A)

Time synchronization has two general approches;
Separate synchronization pulse - separate wire for all the IEDs
Using communication buses- master clock broadcast time telegrams and slaves regularly ask for time

Functions and Protocols in the OSI Model

 Application Layer

The protocols at the application layer handle file transfer, virtual terminals, network management, and fulfilling networking requests of applications. A few of the protocols
that work at this layer include:
• File Transfer Protocol (FTP)
• Trivial File Transfer Protocol (TFTP)
• Simple Network Management Protocol (SNMP)
• Simple Mail Transfer Protocol (SMTP)
• Telnet
• Hypertext Transfer Protocol (HTTP)

Presentation
The services of the presentation layer handle translation into standard formats, data compression and decompression, and data encryption and decryption. No protocols work at this layer, just services. The following lists some of the presentation layer standards:
• American Standard Code for Information Interchange (ASCII)
• Extended Binary-Coded Decimal Interchange Mode (EBCDIC)
• Tagged Image File Format (TIFF)
• Joint Photographic Experts Group (JPEG)
• Motion Picture Experts Group (MPEG)
• Musical Instrument Digital Interface (MIDI)

Session
The session layer protocols set up connections between applications, maintain dialog control, and negotiate, establish, maintain, and tear down the communication channel.
Some of the protocols that work at this layer include:
• Network File System (NFS)
• NetBIOS
• Structured Query Language (SQL)
• Remote procedure call (RPC)

Transport
The protocols at the transport layer handle end-to-end transmission and segmentation into a data stream. The following protocols work at this layer:
• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
• Secure Sockets Layer (SSL)/Transport Layer Security (TLS)
• Sequenced Packet Exchange (SPX)

Network
The responsibilities of the network layer protocols include internetworking service, addressing, and routing. The following lists some of the protocols that work at this layer:
• Internet Protocol (IP)
• Internet Control Message Protocol (ICMP)
• Internet Group Management Protocol (IGMP)
• Routing Information Protocol (RIP)
• Open Shortest Path First (OSPF)
• Novel Internetwork Packet Exchange (IPX)

Data Link
The protocols at the data link layer convert data into LAN or WAN frames for transmission, convert messages into bits, and define how a computer accesses a network. This layer is divided into the Logical Link Control (LLC) and the Media Access Control (MAC) sublayers. Some protocols that work at this layer include the following:
• Address Resolution Protocol (ARP)
• Reverse Address Resolution Protocol (RARP)
• Point-to-Point Protocol (PPP)
• Serial Line Internet Protocol (SLIP)

Physical
Network interface cards and drivers convert bits into electrical signals and control the physical aspects of data transmission, including optical, electrical, and mechanical requirements.
The following are some of the standard interfaces at this layer:
• High-Speed Serial Interface (HSSI)
• X.21
• EIA/TIA-232 and EIA/TIA-449

RTU and Substation automation

Remote Terminal Unit (RTU) lies between the substation and the network controlling center(NCC). Basically RTU interfaces the devices in the physical world to the SCADA. An RTU can be interfaced with the Central Station with different communication media (usually serial (RS232, RS485, RS422) or Ethernet). RTU can support standard protocols (Modbus, IEC 60870-5-101/103/104, DNP3, ICCP, etc.) to interface any third party software. 

Common Data classes

IEC 61850-7-3 defines common data classes for a wide range of well known applications. The
core common data classes are classified into the following groups:

– status information,
– measurand information
– controllable status information,
– controllable analogue information,
– status settings,
– analogue settings
– description information.

There are services to exchange these data.The services defined in IEC 61850-7-2 are called abstract services.

The four main building blocks of the Substation Automation System

• the substation automation system specific information models(logical nodes and data)
• the information exchange methods(interface)
• the mapping to concrete communication protocols, (mapping to MMS and TCP/IP)
• the configuration of a substation IED.

Access Control Administration

Once an organization develops a security policy, supporting procedures, standards, and guidelines, it must choose the type of access control model: DAC, MAC, or role-based. After choosing a model, the organization must select and implement different access control technologies and techniques. Access control matrices, restricted interfaces, and content-dependent, context-dependent, and rule-based controls are just a few of the choices.

Centralized Access Control Administration

AAA protocol is the authentication protocol used,  AAA stands for authentication, authorization, and auditing.Depending upon the protocol, there are different ways to authenticate a user in this client/server architecture. The traditional authentication protocols are Password Authentication Protocol (PAP), Challenge Handshake Authentication Protocol (CHAP), and a newer method referred to as Extensible Authentication Protocol (EAP).

Remote Authentication Dial-In User Service (RADIUS) is a network protocol and provides client/server authentication and authorization, and audits remote users. RADIUS uses UPD. Terminal Access Controller Access Control System (TACACS) provide same functionality as RADIUS with a few differences
in some of its characteristics.TACACS uses TCP.  RADIUS encrypts the user’s password only as it is being transmitted from the RADIUS client to the RADIUS server. Other information, as in the username, accounting, and authorized services, is passed in cleartext.  TACACS+ encrypts all of this data between the client and server and thus does not have the vulnerabilities inherent in the RADIUS protocol.

RADIUS is the appropriate protocol when simplistic username/password authentication can take place and users only need an Accept or Deny for obtaining access, as in ISPs. TACACS+ is the better choice for environments that require more sophisticated authentication steps and tighter control over more complex authorization activities, as in corporate networks.

Diameter is another AAA protocol that provides the same type of functionality as RADIUS and TACACS+ but also provides more flexibility and capabilities to meet the new demands of today’s complex and diverse networks. RADIUS and TACACS+ are client/server protocols, which means the server portion cannot send unsolicited commands to the client portion.Diameter is a peer-based protocol that allows either end to initiate communication.

Decentralized Access Control Administration

A decentralized access control administration method gives control of access to the people closer to the resources—the people who may better understand who should and should not have access to certain files, data, and resources. But centralized Access Control Administration is recommended in implementations to maintain the privacy of the system.

Access Control Models

The main characteristics of the three different access control models are important to understand.

• DAC (Discretionary Access Control) Data owners decide who has access to resources, and ACLs are used to enforce the security policy.
• MAC(Mandatory Access Control) Operating systems enforce the system’s security policy through the use of security labels. Eg: security clearance,In a military environment, the classifications
  could be top secret, secret, confidential, and unclassified.A commercial organization might use confidential, proprietary, corporate, and sensitive.
• RBAC(Role-Based Access Control) Access decisions are based on each subject’s role and/or functional position.

Once an organization determines what type of access control model it is going to use, it needs to identify and refine its technologies and techniques to support that model.

Access Control Techniques

Access control techniques are used to support the access control models.

• Access control matrix Table of subjects and objects that outlines their access relationships
• ACL Bound to an object and indicates what subjects can access it
• Capability table Bound to a subject and indicates what objects that subject can access
• Content-based access Bases access decisions on the sensitivity of the data, not solely on subject identity
• Context-based access Bases access decisions on the state of the situation, not solely on identity or content sensitivity
• Restricted interface Limits the user’s environment within the system, thus limiting access to objects
• Rule-based access Restricts subjects’ access attempts by predefined rules

Single Sign On(SSO) Technologies

If the user has to enter different User ID and User password every time he access a service like printer, file server, it becomes overhead to the user to remember all the usernames and passwords. They tend to write them down and then the security is exposed. Managing user password and renewing them is an overhead to the administrators too. If user has to remember on password only enforce more security in to that password using longer passwords with higher entropy.  SSO offers one time user authentication (User ID and Password) and he is good to access all the services. One bottleneck in achieving SSO is the inadequate system interoperability of services.

Examples of Single Sign-On Technologies 

• Kerberos Authentication protocol that uses a KDC (Key Distribution center) and tickets, and is based on symmetric key cryptography 
• SESAME(Secure European System for Applications in a Multi-vendor Environment) Authentication protocol that uses a PAS(Privileged attribute server like KDC) and PACs(Privileged attribute certificates), and is based on symmetric and asymmetric cryptography 
• Security domains Resources working under the same security policy and managed by the same group 
• Thin clients Terminals that rely upon a central server for access control, processing, and storage

Access control and markup languages

Organizations need a way to control how their information is used internally within their applications. Extensible Markup Language (XML) is the standard that provides the meta data structures to allow this expression of data. Organizations need to be able to communicate their information, and since XML is a global standard, as long as they both follow the XML rules, they can exchange data back and forth.Users on the sender’s side need to be able to access services on the receiver’s side, which the Service Provisioning Markup Language (SPML) provides. The receiving side needs to make sure the user who is making the request is properly authenticated by the sending company before allowing access to the requested service, which is provided by the Security Assertion Markup Language (SAML). To ensure that the sending and receiving companies follow the same security rules, they must follow the same security policies, which is the functionality that the extensible Access Control Markup Language (XACML) provides.

Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks. It relies on Extensible Markup Language (XML) for its message format, and usually relies on other Application Layer protocols, most notably Remote Procedure Call (RPC) and Hypertext Transfer Protocol (HTTP), for message negotiation and transmission.

This XML based protocol consists of three parts: an envelope(which defines what is in the message and how to process it),header and body.